There is a vanilla mechanic to turn villagers into zombies to cure them later (for better trades).
With default configs villagers just die instead of turning into zombies.
Removing minecraft:zombie_villager from HostileMobsList in /config/adaptive_performance_tweaks/spawn/MinecraftSpawn.toml solved the issue immediately.

Added:
Actually, this wasn't enough. I had to add allowList = ["minecraft:villager", "minecraft:zombie_villager"] into [General] section of spawn.toml. And I think there is no need to touch HostileMobsList at all in this case as spawn.toml settings are more global and override everything.

Thanks a lot for the report. I will try if I could track all villagers and ignore them if they are turned into zombies.

The fix should be live in the next hours.

Please keep in mind that even if it allows Zombification, it could be that the new Zombie Villager (with a different ID) is remove afterwards when the server load is to high or to many Zombie Villagers are already spawned.

[15:15:19] [Server thread/DEBUG] [APTweaks(Spawn)/]: [Zombie Villager Conversion] Convert Villager['Villager'/360, l='ServerLevel[world]', x=22.85, y=143.00, z=-598.90] to entity.minecraft.zombie_villager
[15:15:19] [Server thread/DEBUG] [APTweaks(Spawn)/]: [Zombie Villager Conversion] Allow join event for ZombieVillager['Zombie Villager'/376, l='ServerLevel[world]', x=22.85, y=143.00, z=-598.90] in minecraft:overworld