The gamerule doMobSpawning set to false, however, zombies will still spawn near a villager. The gamerule doDaylightCycle was set to false as well, and the issue occurred when changing the time manually from noon (and day) to midnight. The problem happened more than once when changing the time, however, once the zombie cap was reached and they were killed, no more spawned. Only a new night would make more zombies spawn. The world is a redstone ready superflat preset with only 1 villager present.