Networking Issues on Windows Holographic Version(21H1)?

Question

Since a while I am working with HoloLens2. My last OS-Versions were 10.0.18362.1005 and 10.0.19041.1109. I am developing with Unity 2019.4.7. My whole code was and still is running great on those old OS-Versions. Now I updated to OS-Version 21H1 and I have huge problems with everything including networking. For example, my Mixed-Reality-WebRTC Pluging (from Microsoft), which only supports ARM-Architecture, does not work anymore on my new Device. The app crashes after it was successfully starting.
Another thing is, that the DevicePortal does not transmit virtual inputs. Again, on my older HoloLens2´s Virtual Input works great.

Also, even if I disable WebRTC parts of my Project, I still get Exceptions somewhere in my Networking-System which I can´t assign to any cause. But it looks like it has to do anything with my Networking-Thread, which receives and sends big UDP-DataStructures and deserializes them. The exception is like this:

System.Runtime.ExceptionServices.ExceptionDispatchInfo.throw()(at...)
System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(System.Threading.Tasks.Task task)(at...)
System Runtime CompilerServices.ConditionalWeakTable´2[TKey, TValue]..ctor() (at...)
MyUDPCommunicator+<>c_DisplayClass19_0.<Send>b__0() (at...)
System-Runtime.CompilerServices.AsyncMethodBuilderCore+MoveNextRunner.InvokeMoveNext(System.Object stateMachine) (at...)
UnityEngine.AudioClip+PCMReaterCallback.Invoke (System.Single[] data)(at...)
System.Threading.ExecutionContext.RunInternal (System.Threading.ExecuteContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean.preserveSyncCtx) (at...)
and so on .. (if you need full stackTrace, please let me know)

I would be really glad if anybody could help me with this. Is OS-Version 21H1 restricted to any specific Unity-Version or VisualStudio Version (here currently I use 16.4.5)? Or is it Restricted to specific Networking Libraries? Thanks in advance!