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).