Villagers dissapearing

So I had this villager farm with tons of villagers that i breeded. I had them locked in in a room with the only entrence being an iron door and it worked for a super long time but one day I went to the nether and mined and when i got back to traid emeralds they where all just gone... they have probably despawned or something. I would really appreciate if i could get the villagers back since I really liked that world and i am 100% sure there was no opening. And i had a bell, working stations and beds for all villagers so there would be no reason for them to escape either. This must be a bug insce im playing in the beta and i really hope i can get my villagers back in some way because I really enjoyed the farm.