Aaron Graham

@Samuel Bignell, Unfortunately I can confirm that workaround does not work. The last time I lost progress due to this bug, I was building a gold farm in the nether. I was periodically going back and forth between the nether and the overworld. I was the only player on the server that evening. I logged off in the overworld and when I checked the next morning all of my progress in the nether was lost.

My experience when playing on my friend's realm is that the game won't crash. It appears to play normally, but when I log off and come back several hours later, it will have lost hours of progress. I will immediately know when it has happened because it will spawn me in different place in the world than from where I logged out.  This has happened to me 3 times in the last 4 days and never happened once before 1.16. Several of the other members of the realm have also had it happen to them. It is frustrating to lose hours worth of work.

John: I've updated this bug report's summary and description to refer to all baby mobs. Thank you for the suggestion. I've also attached another screenshot showing the same behavior with sheep. I suspect that Mojang may have done this intentionally to avoid cases where a mob becomes an adult in a confined space (low ceiling) which then causes them to take suffocation damage and die. That should be avoidable if they prevent the mob from growing from a baby to an adult if there is not sufficient headroom. This would also let players create galleries of baby animals that never grow up.