I'm in the middle of trying to muck with FAPro because I have my own license and I'm using v7.x. No joy so far but my plan was to figure that out on my own. Having said that, I toggled to use the external viewer, and when I toggled back to internal I got this error log entry. Just sharing in case it's something you want to investigate, not looking for anything myself.

9/24/2026 3:40:41 PM - App: Object reference not set to an instance of an object.
Object reference not set to an instance of an object.
Documentation Monster v0.5.4.5
10.0.20348.1.amd64fre.fe_release.210507-1500 - en-US - NET .NET 10.0.12 - 64 bit
Amazon EC2 r7iz.2xlarge, Microsoft Remote Display Adapter, hw-acc: True
WebView: rt: 153.0.4234.48 - sdk: 1.0.4022.49
en-US - en-US
c:\Program Files\Documentation Monster
Portable: False
---
DocumentationMonster
   at MarkdownMonster.Windows.PreviewBrowser.WebViewPreviewControl.PreviewMarkdown(MarkdownDocumentEditor editor, Boolean keepScrollPosition, Boolean showInBrowser, String renderedHtml, Int32 editorLineNumber) in D:\projects\DocumentationMonster\DocumentationMonster\Windows\PreviewBrowser\WebViewPreviewControl.xaml.cs:line 75
   at MarkdownMonster.MainWindow.PreviewMarkdown(MarkdownDocumentEditor editor, Boolean keepScrollPosition, Boolean showInBrowser, String renderedHtml, Int32 editorLineNumber) in D:\projects\DocumentationMonster\DocumentationMonster\MainWindow.xaml.cs:line 2827
   at MarkdownMonster.AppCommands.<>c__DisplayClass111_0.<TogglePreviewBrowser>b__0(Object p, ICommand e) in D:\projects\DocumentationMonster\DocumentationMonster\_Classes\Commands\AppCommands.cs:line 1241
   at MarkdownMonster.CommandBase.Execute(Object parameter) in D:\projects\DocumentationMonster\DocumentationMonster\Controls\CommandBase.cs:line 84
   at MarkdownMonster.AppCommands.<PreviewModes>b__106_0(Object parameter, ICommand command) in D:\projects\DocumentationMonster\DocumentationMonster\_Classes\Commands\AppCommands.cs:line 1209
   at MarkdownMonster.CommandBase.Execute(Object parameter) in D:\projects\DocumentationMonster\DocumentationMonster\Controls\CommandBase.cs:line 84
   at MS.Internal.Commands.CommandHelpers.CriticalExecuteCommandSource(ICommandSource commandSource, Boolean userInitiated)
   at System.Windows.Controls.MenuItem.InvokeClickAfterRender(Object arg)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
System.NullReferenceException
---------------------------

I think that's likely a timing error where the toggle isn't quick enough to get the control up and running.

Added an additional check that will not fire the preview if the browser is not there yet. I'm pretty sure there will be another refresh later that properly updates the view.

+++ Rick ---

Thanks for all the back and forth today. I'm feeling pretty good about the migration and excited to be moving away from WWHB after years of dedicated service. It can go retire upstate now and get plenty of fresh air and exercise. 😃