In my Minecraft world, I have a villager trading hall with about 20 librarians. My understanding with villagers is that when they have a profession, they are assigned a profession block if there is one available. Also, I understand that in order to refresh their trades, they must be able to access there profession block. So, I set my trading hall up accordingly so that every villager has access to their profession block. However, I have been running into this incredibly frustrating problem in that they have been randomly switching the specific lectern they are assigned to. This change is not triggered by a factor I believe to have created, and my research has backed that up. I could get around this issue by putting all the villagers in one room so that they have access to every lectern when they do switch, however, this is an inconvenience as I am under the impression that they will refresh their trades at a faster rate if they are in close proximity to there profession block. Nothing I have found in the Minecraft Wiki or any other source states that villagers will swap profession blocks, so I believe this is a glitch that needs immediate attention.