ProStartPageConfig crashes when loading add-ins side-by-side

[mahj]

Hi,

When running ProStartPageConfig in the ArcGIS Pro Add-In Samples (https://github.com/Esri/arcgis-pro-sdk-community-samples/) in ArcGIS Pro 3.6 with the Add-In Manager option "Load add-ins side by side" checked it crashes with the following unhandled exception:

System.Windows.Markup.XamlParseException: ''Add value to collection of type 'Microsoft.Xaml.Behaviors.BehaviorCollection' threw an exception.' Line number '212' and line position '14'.'

Inner Exception
''Add value to collection of type 'Microsoft.Xaml.Behaviors.BehaviorCollection' threw an exception.' Line number '212' and line position '14'.'

Any idea how this can be fixed?

Thanks,
Markus