I agree with IllagerCaptain. MCPE-233088 seems to be a grab bag of related but distinct splitscreen issues, as decribed in the comments. I reported this for Realms (REALMS-13753).
I reported this new iteration of splitscreen Realm bug over a week ago under Realms (REALMS-13753), but it was marked as a duplicate. I am not sure if this is the thread that is the duplicate, but it seems several related but slightly different issues are ending up pooled here but all under splitscreen issues.
My experience is as decribed most recently by Hacker1MC: “The secondary player joins under their correct username, but not with the correct player ID or data. They appear at world spawn, empty inventory, and notably they are a new player ID, as opposed to a repeat of the ID created in June 2025.” I have not confirmed “new player ID" (not sure how on XBox), but the other behavior is the same.
Merry Christmas! My son is on holiday break, and we don't get to play together…
It works now!
Bug REALMS-13024 was incorrectly marked as a duplicate of this bug. It is a different issue. It is unclear if they are related on the backend, but the behavior is different on our Xbox. The issue in REALMS-13024 prevents a second account from joining split screen on a realm at all. It throws the error and causes first player to leave the realm and being completely unable to play together. The bug here (222048) appears to be related to assigning the second player as guest (it seems on a local world) but they can still play.
This is not a duplicate. MCPE-222048 is a different issue. It is unclear if they are related on the backend, but the behavior is different on our Xbox. The current issue prevents a second account from joining split screen on a realm at all. It throws the error and causes first player to leave the realm and being completely unable to play together. The 222048 bug is related to assigning the second player as guest (it seems on a local world) but they can still play.
Related to: MCPE-233088 , which describes the recent issue distinct from the origins of this thread.