Village leader changes seemingly at random

I constructed an iron farm in my realm that uses villagers. I built a breeder (100+ blocks away) which produces clean villagers, and sends them through the nether to the iron farm, where beds are waiting (no workstations or bells). When they link to their beds and sleep, I placed and broke the bell to locate the leader. I then transported the leader and his bed to the center of the farm. The farm began producing iron golems, and working for several hours. Suddenly, iron golems began spawning outside of the farm. I broke the bell and replaced it, and the leader had changed. This has happened multiple times