I tried using my convertor to zombify and cure some new villagers, which was working last night, but this time after the villager turned into a zombie, I couldn't get it to get back into the minecart. It jumped right out and started attacking the rest of my villagers in the convertor, but instead of also zombifying them, they just straight up died. I tried it multiple times today, all providing the same results, and as I said, it was just working last night. The realm is completely vanilla.