Villagers disappearing

Villagers in my constructed village will randomly start disappearing. Usually 1 or 2 at a time. My village is well lit, walled off, and has 2 iron golems patrolling around. There are no hazards or ledges to fall from and I sleep through any lightning storms. I don't know where they go but remaining villagers keep breeding to keep the population but there's no evidence to a villager dyeing. What's going on?