Named and bred mobs have been disappearing/despawning. Cows, chickens, bees, and axolotyls. Cows chickens were bred, bees were named, Axolotyls were placed via bucket and named and still disappeared with no death tags seen in chat.
Environment
In jungle biome, all mobs were in some sort of containment/room.
Brianna De Nubilo
This issue is being tracked at MCPE-191623.