1.16.1 server villagers forget their professions levels

Sometimes villagers will forget the profession level they had (Master, for example) and go back down to the beginner level (no XP)… Not sure why this happens or how. It just happens from time to time. Seems to happen after I’ve been offline and unloaded my base.

Nothing unusual about the setup I think. Just placed the jobsite blocks (like a brewing stand) inside the homes of the naturally spawned village.

Typing /version shows:
but I couldn’t find any topics related to villager breeding.

Mojang didn’t want to look at the issue as the server had Paper.