IsEditorOnly is not reflected in grandchild actor when parent/child/grandchild are constructed with ChildActorComponent. This causes the issue that actor will increase incorrect when save the level.
Change the following code in ChildActorComponent.cpp.
When see the World Outliner, the Actor (BP_GrandChild) has increased on the level.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-85478 in the post.