I had went to the Nether dimension and explored through a portal I had already gone through a couple of times. Logged off and shut down my Xbox. Returned the next day, exploring some more. I then returned to the overworld.

All my breeded villagers, original villagers from the village, and animals had despawned: my 10+ maxed level traded librarian, Toolsmith, Weaponsmith, and Armorer villagers, 20+ Cows, 20+ Sheep, and 10+ Chickens.

I had expected everyone, villagers and breeded animals, to still be there as they always have been.

Also my 3 skeleton horses I had leaded to a fence had despawned as well. Only my Fletcher, detached from the village and far far away from it, had remained.