This bug was observed in Bedrock 1.9.83 through to 1.20.40

A villager with a profession but prior to being made permanent by a trade can have their profession made permanent if the player logs out of Realms or (occasionally) unloads the villager through movement.  Once this happens, the villager profession is permanent.

When this bug interacts with MCPE-176341, the result is that villagers will inadvertently make connections to occupied jobsites, and then become trapped in that profession. This can then lead to a propagation of villagers with a fixed profession and no connection to a jobsite.