Related to issue MCCE-6766 which is marked as resolved, but is still occurring on PC.

Was playing Realms today, had my donkey in a boat, put it next to a shallow-ish bit of water (with my character IN the boat) before save/quiting, came back and my donkey and boat were completely gone - my character was at the bottom of the ocean, starting to drown.

Using backups - none of the backups had the Donkey or the boat for over 40 minutes.  Last save WITH the donkey/boat, was when I was OUT of the boat.

This is just today - - recently Realms decided my Anvil didn't deserve to exist (just vanished from my build home), and my co-player reported to me that several of her cows had vanished from their locked/enclosed pens.

Let me know if you need any further detail.