In my Realem (if longer nobody is online) the Villager reset their trade status to 0 and lose their job because of this. (maybe because of the vilager sleeping in a bed ? or too mutch villager workstations?
Edit:
How it happend: imported a survaival world (1 texturepacket that changes the villager gui: https://mcpedl.com/trading-plus/ ) just play normal survival content had lots of villager healed zombies and normal villager and more workstaions then i need.my friend also traded a lot with them until they lost jobs even they had been already trading with them in multiplayer (no cheats activdet).
Also sry for bad englisch i am german i try my best.