This project does not have HLODs built in, so I don’t think the problem has anything to do with that.
The problem is also not related to using specific Fortnite assets such as Asteria Trees or similar; our map is almost entirely built with exported models.
Unchecking World Streaming does not seem to solve the problem.
I’ll check the Sequences to see if any are empty. Thank you very much for your advice and suggestions 
!!