I gathered 2 cows and breed them till I got about ten. Logged out for 7 hours to sleep and in morning when I returned they were gone, Server auto reboots at midnight to help with the lag I had been getting. I rolled back to the last backup which was 4am EST and server had already rebooted at midnight. The cows returned from the restore. but they should never had despawned
MC-87483
Cows de-spawning
Resolved
Duplicate
1
Can confirm, happened to me. May be happening with other mobs as well (I've had villagers despawn twice now).
Edit: OK, this is strange. I was playing on a multiplayer server when this happened. The server rebooted, and now the cows (and villagers) are back again. I'd like to test this some more, but it may be difficult to reproduce.