HLOD state is not cleared when moving to a scene without HLOD so primitives may read the state from the old scene and incorrectly cull objects. The safe fix is to clear the HLOD state maps when the LODTree is inactive.
Swap between a level with HLOD and one without, objects may re-use the stale visibility state as it is not cleared per level.
Unknown repro rate.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-64432 in the post.