Streaming a level back in before it finishes streaming out behaves undesirably.
When a level is streamed out the actors/components in the level are incrementally unregistered over multiple frames. Once everything unregisters the actors are all EndPlayed (at which point they stop ticking) and then they sit around waiting for GC to scoop them. If the level streams back in before the stream out process completes- the existing level will be re-used and the actors inside of it will re-register their components and begin play again in whatever state they were in when they unregistered/ended play.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-90441 in the post.