It seems that the last build/cook i.e. by using Launch Session could fail and trigger this non-intuitive state of Project Moderation Warning upon the (any) next start of the Editor when opening your Project map.
Perhaps like in my case, take a close look at the Asset Check and UEFN Validation categories in the local Message Log (not the Portal) after launching a test session. This might reveal error(s) that cause the Moderation warning (for all of your session). I removed an illegal reference from some material instance, saved my changes, launched and after successful playtest the project can now be opened without any warning.
This was a technical issue rather than a functional violation of the Epic Content Guidelines IMHO.