Today when running the designer 5.6 (5.6.0) RTM Build Date: 20-Aug-2019 The app started then disappeared without and error. On the second run I received this stack trace and after answering continue in the error dialog the screen whose image I've attached.

On the 3rd run all seemed to be ok.

See the end of this message for details on invoking 
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.ArgumentException: Parameter is not valid.
   at System.Drawing.Graphics.get_PageUnit()
   at DevExpress.Utils.Paint.XPaint.CalcDefaultTextSize(Graphics g, Font font)
   at DevExpress.XtraEditors.ViewInfo.BaseControlViewInfo.CalcTextSizeCore(GraphicsCache cache, String text, Int32 maxWidth)
   at DevExpress.XtraEditors.ViewInfo.BaseControlViewInfo.CalcTextSizeCore(Graphics g, String text, Int32 maxWidth)
   at DevExpress.XtraEditors.ViewInfo.BaseControlViewInfo.CalcTextSize(Graphics g, Boolean useDisplayText)
   at DevExpress.XtraEditors.ViewInfo.BaseButtonViewInfo.CalcTextBounds(Graphics gr)
   at DevExpress.XtraEditors.BaseControl.UpdateViewInfo(Graphics g)
   at DevExpress.XtraEditors.BaseButton.OnPaintBackground(PaintEventArgs e)
   at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
   at System.Windows.Forms.Control.WmPaint(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at DevExpress.Utils.Controls.ControlBase.WndProc(Message& m)
   at DevExpress.XtraEditors.BaseControl.WndProc(Message& msg)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.4121.0 built by: NET48REL1LAST_C
    CodeBase: file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/mscorlib.dll
----------------------------------------
LLBLGenPro
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/LLBLGenPro.exe
----------------------------------------
System
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.4001.0 built by: NET48REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
DevExpress.Data.v19.1
    Assembly Version: 19.1.5.0
    Win32 Version: 19.1.5.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/DevExpress.Data.v19.1.DLL
----------------------------------------
System.Core
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.4121.0 built by: NET48REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Core/v4.0_4.0.0.0__b77a5c561934e089/System.Core.dll
----------------------------------------
System.Windows.Forms
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.4121.0 built by: NET48REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
SD.Tools.Algorithmia
    Assembly Version: 1.4.0.0
    Win32 Version: 1.4.19.0711
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/SD.Tools.Algorithmia.DLL
----------------------------------------
SD.LLBLGen.Pro.ApplicationCore
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/SD.LLBLGen.Pro.ApplicationCore.DLL
----------------------------------------
System.Configuration
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Configuration/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Xml
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Xml/v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
SD.LLBLGen.Pro.DBDriverCore
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/SD.LLBLGen.Pro.DBDriverCore.DLL
----------------------------------------
System.Security
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Security/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Security.dll
----------------------------------------
SD.LLBLGen.Pro.Core
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/SD.LLBLGen.Pro.Core.DLL
----------------------------------------
DevExpress.Utils.v19.1
    Assembly Version: 19.1.5.0
    Win32 Version: 19.1.5.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/DevExpress.Utils.v19.1.DLL
----------------------------------------
SD.LLBLGen.Pro.VSNetIntegrationSupport
    Assembly Version: 5.0.0.0
    Win32 Version: 5.0.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/SD.LLBLGen.Pro.VSNetIntegrationSupport.DLL
----------------------------------------
Accessibility
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/Accessibility/v4.0_4.0.0.0__b03f5f7f11d50a3a/Accessibility.dll
----------------------------------------
ActiproSoftware.SyntaxEditor.Net20
    Assembly Version: 4.0.290.0
    Win32 Version: 4.0.290.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/ActiproSoftware.SyntaxEditor.Net20.DLL
----------------------------------------
ActiproSoftware.Shared.Net20
    Assembly Version: 1.0.104.0
    Win32 Version: 1.0.104.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/ActiproSoftware.Shared.Net20.DLL
----------------------------------------
SD.Tools.BCLExtensions
    Assembly Version: 1.2.2.0
    Win32 Version: 1.2.18.1022
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/SD.Tools.BCLExtensions.DLL
----------------------------------------
SD.Frameworks.Validation.DocumentDatabase
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Derived%20Models/SD.Frameworks.Validation.DocumentDatabase.dll
----------------------------------------
SD.LLBLGen.Pro.Importers
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Plugins/SD.LLBLGen.Pro.Importers.DLL
----------------------------------------
System.Data.Entity
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Data.Entity/v4.0_4.0.0.0__b77a5c561934e089/System.Data.Entity.dll
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.AccessDBDriver
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/Access/SD.LLBLGen.Pro.DBDrivers.AccessDBDriver.DLL
----------------------------------------
System.Design
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Design/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Design.dll
----------------------------------------
SD.LLBLGen.Pro.TypeConverters
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/TypeConverters/SD.LLBLGen.Pro.TypeConverters.DLL
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkCorev1
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkCorev1.dll
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkCorev21
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkCorev21.dll
----------------------------------------
SD.LLBLGen.Pro.Plugins
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Plugins/SD.LLBLGen.Pro.Plugins.DLL
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkCorev2
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkCorev2.DLL
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.DB2DBDriver
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/DB2/SD.LLBLGen.Pro.DBDrivers.DB2DBDriver.DLL
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkCorev22
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkCorev22.dll
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkv1
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkv1.dll
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkv4
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkv4.dll
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkv5
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkv5.dll
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.FirebirdDBDriver
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/Firebird/SD.LLBLGen.Pro.DBDrivers.FirebirdDBDriver.DLL
----------------------------------------
SD.Frameworks.Validation.EntityFrameworkv6
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Entity%20Framework/SD.Frameworks.Validation.EntityFrameworkv6.dll
----------------------------------------
SD.Frameworks.Validation.LinqToSql
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/Linq%20to%20Sql/SD.Frameworks.Validation.LinqToSql.dll
----------------------------------------
SD.Frameworks.Validation.LLBLGenPro
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/LLBLGen%20Pro/SD.Frameworks.Validation.LLBLGenPro.dll
----------------------------------------
SD.Frameworks.Validation.NHibernate
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Frameworks/NHibernate/SD.Frameworks.Validation.NHibernate.dll
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.MySqlDBDriver
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/MySql/SD.LLBLGen.Pro.DBDrivers.MySqlDBDriver.DLL
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.OracleDBDriver_MSOracle
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/OracleMSOracle/SD.LLBLGen.Pro.DBDrivers.OracleDBDriver_MSOracle.DLL
----------------------------------------
System.Data
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.4121.0 built by: NET48REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_64/System.Data/v4.0_4.0.0.0__b77a5c561934e089/System.Data.dll
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.OracleDBDriver_ODPNET
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/OracleODPNET/SD.LLBLGen.Pro.DBDrivers.OracleDBDriver_ODPNET.DLL
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.PostgreSqlDBDriver
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/PostgreSql/SD.LLBLGen.Pro.DBDrivers.PostgreSqlDBDriver.DLL
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.SpannerDBDriver
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/Spanner/SD.LLBLGen.Pro.DBDrivers.SpannerDBDriver.dll
----------------------------------------
SD.LLBLGen.Pro.DBDrivers.SqlServerDBDriver
    Assembly Version: 5.6.0.0
    Win32 Version: 5.6.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/Drivers/SqlServer/SD.LLBLGen.Pro.DBDrivers.SqlServerDBDriver.DLL
----------------------------------------
DevExpress.XtraEditors.v19.1
    Assembly Version: 19.1.5.0
    Win32 Version: 19.1.5.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/DevExpress.XtraEditors.v19.1.DLL
----------------------------------------
DevExpress.XtraGrid.v19.1
    Assembly Version: 19.1.5.0
    Win32 Version: 19.1.5.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/DevExpress.XtraGrid.v19.1.DLL
----------------------------------------
DevExpress.XtraLayout.v19.1
    Assembly Version: 19.1.5.0
    Win32 Version: 19.1.5.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/DevExpress.XtraLayout.v19.1.DLL
----------------------------------------
Microsoft.VisualBasic
    Assembly Version: 10.0.0.0
    Win32 Version: 14.8.3752.0 built by: NET48REL1
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/Microsoft.VisualBasic/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft.VisualBasic.dll
----------------------------------------
Anonymously Hosted DynamicMethods Assembly
    Assembly Version: 0.0.0.0
    Win32 Version: 4.8.4121.0 built by: NET48REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_64/mscorlib/v4.0_4.0.0.0__b77a5c561934e089/mscorlib.dll
----------------------------------------
System.ComponentModel.DataAnnotations
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.ComponentModel.DataAnnotations/v4.0_4.0.0.0__31bf3856ad364e35/System.ComponentModel.DataAnnotations.dll
----------------------------------------
System.Data.Linq
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.3752.0
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Data.Linq/v4.0_4.0.0.0__b77a5c561934e089/System.Data.Linq.dll
----------------------------------------
UIAutomationClient
    Assembly Version: 4.0.0.0
    Win32 Version: 4.8.4121.0 built by: NET48REL1LAST_C
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/UIAutomationClient/v4.0_4.0.0.0__31bf3856ad364e35/UIAutomationClient.dll
----------------------------------------
DevExpress.XtraBars.v19.1
    Assembly Version: 19.1.5.0
    Win32 Version: 19.1.5.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/DevExpress.XtraBars.v19.1.DLL
----------------------------------------
ActiproSoftware.WinUICore.Net20
    Assembly Version: 1.0.104.0
    Win32 Version: 1.0.104.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/ActiproSoftware.WinUICore.Net20.DLL
----------------------------------------
ActiproSoftware.SyntaxEditor.Addons.DotNet.Net20
    Assembly Version: 4.0.290.0
    Win32 Version: 4.0.290.0
    CodeBase: file:///C:/Program%20Files%20(x86)/Solutions%20Design/LLBLGen%20Pro%20v5.6/ActiproSoftware.SyntaxEditor.Addons.DotNet.Net20.DLL
----------------------------------------

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
    <system.windows.forms jitDebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.

It's an issue with the startup code which runs things in parallel, which should be OK according to devexpress but apparently sometimes it fails. We've mitigated it to a point where we can't reproduce it anymore no matter how hard we try or which hardware we use, could you try 5.6.2 to see if that solves the problem for you? As we can't reproduce it ourselves it's hard to pinpoint what it can be.

If you can still reproduce it in 5.6.2, we'll remove the parallel startup code and will re-introduce sequential startup code to get rid of this. What we're doing currently is opening the main window on its own main thread (also STA) when the startup dialog is opened so it opens instantly when you e.g. select a project.

Thanks in advance for testing.