Looks like the replication system doesn't properly account for bShouldBeVisible. Once a level has be marked bShouldBeVisible=false on the server, the level is completely cleaned up and all actor channels are permanently closed.
The actor channels should be recreated when the level becomes visible again.
Expected: When visibility is re-enabled the streamed level is visible and networking resumes with no issues.
Actual: When visibility is re-enabled replication errors occur because the Actor channels have been destroyed:
LogNet: Server connection received: ActorChannelFailure
LogNet:Warning: UActorChannel::ProcessBunch: SerializeNewActor failed to find/spawn actor.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-43042 in the post.