A ways out from the village center (could be a cause, though when I rang the bell they ran into houses nearby the center, so perhaps a login from the player causes villagers too far away from the village center, with proficiencies/jobs to not allow trade?), when clicking on a villager to trade with them, in 1.14.3 it would instantly exit the menu, not allowing trade. This didn't affect all villagers and the majority still allow trade (15-20) while a small outlier didn't (3-5).
Related issues
duplicates
Comments
migrated
migrated
This happens to me too. From what I can tell, it happens when the villager walks too far away from their worksite and somehow they desync from it, becoming unable to find and work from it again.
migrated
Confirmed. This seems to happen to villagers you've levelled up.