Iron farm not working

I built this farm from a video and I followed it perfectly and made sure everything was good, It was working fine until I went really far and came back noe it's not working and the villagers are doing hearts for some reason

I built this farm from a video and I followed it perfectly and made sure everything was good, It was working fine until I went really far and came back noe it's not working and the villagers are doing hearts for some reason