This might be related to MCPE-21416 but this is about items rather than mobs (we too are having issues with mobs, and it's become far more frequent since 1.18).

We have recently created a new world on our We have a wall of maps in our spawn area on a grid of item frames, showing the area around our spawn. But for the second time in the last week, we've had a map just pop out of existence whilst people aren't around.

We don't think it's getting popped off as no other maps are missing, and it seems to happen when no-one is around. It's very strange.

We also had a diamond Fortune pixaxe just pop out of existence. Logged in, dropped an item into a chest, logged out and the pixaxe disappeared - not in inventory or the chest, whilst other items are still there.

Expect it's not platform-specific, but is to do with the Realms server.