Zombie Villagers are able to be splashed with Weakness, and they then accept the Golden Apple and start shaking indicating they have started the curing process. However, after several minutes, they stop shaking and stop giving of particles but stay as a zombie.

In the images I have attached, I cured all three villagers from zombie, but none of them actually got cured. This has happened multiple times now, with about 5 or 6 different villagers.