Villagers despawning in Nether

The other day, I was transporting a bunch of villagers to the nether to get cured. I got a zombie into the nether no problem.I cured and traded with them, and wen't many time between the nether and overworld, and no problem. Now I even logged off few times, and still problem. But one day I decide to fight the wither. (MCPE-146598), tldr; it despawns. Somehow. So ok, I've lost my stuff and can't find the wither anywhere so I go to get some enchantments from my villagers, but they're gone. Each one, even the zombie, totally gone. I don't have any pets, so I don't know if every mob disappeared, but it might be linked to the wither despawning.