I ran into a crash when updating the Docking.for.Xaml nuget to the latest stable 2021.1.119 version. This doesn't crash in the previous stable 2020.3.1020 version.
Steps to reproduce: create a .NET Core (did not try with .NET Framework because my actual program uses Core) WPF solution in Visual Studio, copy the PaneGroupExtensions class from https://github.com/telerik/xaml-sdk/blob/master/Docking/PaneGroupItemsSource/PaneGroupExtensions.cs and fix the namespace, and also around lines 48-55 don't bother with content or datacontext for the pane. The important thing just is to create a pane and added to the Group.Items collection. Add the Docking nuget package to the project. Then create a simple ViewModel class for your MainWindow with an collection property named "ForExtension" and set it as the DataContext for the MainWindow.
Then add the following simple RadDocking inside your MainWindow.xamls Grid: