I recently experienced possible OneFilePerActor issue which I discovered accidently by using TWeakObjectPtr together with UPROPERTY(EditAnywhere).
- Have C++ component with array of structs containg this property
- Have one file per actor / external actor enabled
- Configure editor to start last opened map in Editor Preferences
- Place actor BPs with this component into level and set the property to reference some other actor in the level.
This will lead to reference being null on next level load when editor starts up. I am not entirely sure which steps are necessary and it can be easily workarounded by not using TWeakObjectPtr which is probably intended way of doing UPROPERTies anyway.