I think I found a bug in all components that use AnimationGroupBase.
How you can reproduce it...
Navigate to a page that has a component that uses AnimationGroupBase - in my case TreeView.
Hit refresh (F5) a couple of times
Wait about 60 seconds and you will get an exception from the title..
The problem is AnimationGroupBase. It has a async void Dispose method. Please fix it to be just void.
Here is a stack trace.
Microsoft.AspNetCore.Components.Server.Circuits.CircuitHost: Error: Unhandled exception in circuit 'uU2u6m_DXs2TW1iUNDEpwJB235BzcJVRHTXjF8kbbaU'.
System.Threading.Tasks.TaskCanceledException: A task was canceled.
at Microsoft.JSInterop.JSRuntime.InvokeWithDefaultCancellation[T](String identifier, Object[] args)
at Telerik.Blazor.Components.AnimationContainer.AnimationGroupBase.Dispose()
at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__139_0(Object state)
at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.ExecuteSynchronously(TaskCompletionSource`1 completion, SendOrPostCallback d, Object state)
at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.<>c.<.cctor>b__23_0(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.ExecuteBackground(WorkItem item)