A villager trading hall created continually breaks because villagers do not keep the same bed. Villagers, at random, will reassign their beds causing iron farms and trades to be affected because villagers cannot sleep due to the reassignment.
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GoldenHelmet
migrated
This issue is tracked at MCPE-46157. Although that ticket refers to workstations, it is the same issue of changing links.
Villagers will de-link from beds and workstations that they cannot reach, but that is intended. A good iron farm tutorial will discuss how to keep them from de-linking. For a trading hall, you actually do not need to give the villagers beds. You can just have one or two villagers with beds to keep the village in existence, and make sure those villagers always have access to their beds.