From the beginning of the plugin, the serialization of villager data was inadequate, which caused errors in the latest versions. Consequently, it was necessary to change the serialization system completely.
Important: Unfortunately, this change is incompatible with previous data, so all villager data will be lost when updating to version 3.3.5 (only for 1.21.8 servers).
This will not happen again in the near future, as the new system uses the API, which also makes serialization much easier.