When migrating to newer versions of the game most of my villagers disappear regardless of if I have traded with them or not, this has been a major problem for me because it has caused my iron farm to break, my villager breeder to break, and for me to lose many of my villagers with important trades like my pumpkin and melon villagers that give me food and my mending and unbreaking villagers. Luckily I made a backup and already got all the other enchants I needed from the other villagers before they disappeared but this will be a huge pain to try and get them back. For reference only three adult villagers and one baby remain and 12 from my iron farm disappeared, 9 from my trading hall are goon and about another 12 from my breeder are gone.