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.
It works now!