Iron farm very slow and rare

Playing on a aternos server with my freinds I have 20 villagers work station and beds I earlier added zombie which worked well but the issue is after sometime the villagers don't sleep and iron farm stops working so I removed them please help

Playing on a aternos server with my freinds I have 20 villagers work station and beds I earlier added zombie which worked well but the issue is after sometime the villagers don't sleep and iron farm stops working so I removed them please help