tl;dr: i had the similar yet different problem, maybe it’s relevant
That’s weird that you mention you having it in 5.3. There was a similar bug with world partition - landscape collision was being lost on streaming out and not being restored on streaming in, also only in packaged build. But it happend on 5.1 and supposed to be fixed on 5.3 (at least i had it fixed this way).
Since it’s likely an engine bug, the first thing i’d try is to test it on the latest engine version, which is currently 5.4.
But seems you don’t use world partition for streaming and instead streaming levels manually, so probably while similar, it’s not exactly the same one. Still, for the referrence, that’s the commit with the fix of the problem for my case. Also i won’t recommend using world partition anytime soon, since it’s still have problems even on 5.4