Bug Ref. script on this Behaviour is missing on recompile!

Every time I rebuild (switch back from VS) on 2019.4.8/win10 while it is running (set to "Stop playing and recompile") the editor throws warnings "The referenced script (Unknown) on this Behaviour is missing!"
This does not happen if I was not running when I recompiled - face palm.

from editor.log

Code (CSharp):

1.  
2. Symbol file LoadedFromMemory doesn't match image D:\project\Library\PackageCache\com.unity.ext.nunit@1.0.0\net35\unity-custom\nunit.framework.dll
3. The referenced script (Unknown) on this Behaviour is missing!
4. (Filename: C:\buildslave\unity\build\Runtime/Scripting/ManagedReference/SerializableManagedRef.cpp Line: 199)
5.