We have a 10-person realm, fully up to date.  People on Xboxes are unable to join the realm immediately upon starting Minecraft.  They are invited and, as the realm owner, I can see that each is a Member of the realm but the realms are not showing in their list.  We’ve found a work around is either to play in a personal world and the realm will appear after a period of time OR if I remove them from the realm member listing and re-invite them.

Once they are in and play, they will follow a normal exit from game, exit from Xbox but when returning they encounter the same issue again: no realms are showing in their list although they are members of the realm.