Villagers that I have traded with unlink from their workstation. I've made a trading hall and made sure that the workstations that the villagers use to refresh their trades is the one placed in front of them. I recently moved this world to a realm but I had this problem before that. To fix it, I have to break all of the work stations an find the villagers who want to link to it. The villagers still have their trades and progression in that trade. I am not certain of this but I think that maybe all of the villagers unlink from their workstations and then link to someone else's workstation.