So i am adding my 2 cts on this issue which haunted me since UE 5.0.0…
This seems to occur also without World Partition. It is enough to just delete some actors and then to wait for some time withut doing anything (maybe 15 minutes or so). The deleted actors suddenly reappear as unloaded.
When I then reopened the level, the unloaded actors were all there and loaded again as if i never deleted them.
This happened with the Thirdperson Template level and the actors which come automatically with it after creating a new Thirdperson project.