Just had an update on Xbox One X with latest Xbox firmware update and this works just like the PC/Android versions.
There was an update to the Island, because under 39.11 you get a message flash up Updating when you click play.
If you still think its here why not put a small example with the Verse custom message and only one room as initially went to rooms 2,3,4 before restarting island.
Jut noticed in your message above you describe Observed and Expected with the same Xbox error are you saying Xbox One, Xbox One X, Xbox Series S, Xbox Series X.
Each one has a diferent loading set and graphic drivers Android works and thats the basis for Nintendo Switch 1.
Still think this has been fixed under 39.11.
In past removing Fortnite completely, deleting cache and reinstalling from the latest version has fixed many problem.
The updates sometimes corrupt the original, especially on big *.00 upgrades.
Even as an indy dev have not got the patience, just dump and reload new Fortnite