For a very long time, Curing Villages has been a problem. If you have multiple Villages and you convert them to zombies at the same time, when you cure them, they change workstations. 

So if you want to cure 3 Zombie Villages with 1 splash potion, Villager 1 could be using Workstation 2, 3 could be using workstation 1. This means the Villagers can't restock their trades. And you need to very slowly convert 1 village at a time. This is an even bigger problem once the gossiping discounts change in the upcoming version (I think this is what I understand is coming to 1.21)

Video examples to come