Great, thanks for the quick update. No more errors with 1.70.4.
FWIW, the error caused other errors with a ScriptableSingleton but I didn't notice anything breaking.
After upgrading to 1.70.3, using Unity 2019.3.0f6, I get following error in the console when playing:
«ReleaseAllScriptCaches did not release all script caches!»
(There's no stack trace or further information.)
Googling the error turns up two issue…