Level 2 (gold badge) villagers change profession and cannot revert

I assigned two villagers as fisherman and farmer, and traded with them to level up and 'lock in' their professions. Despite their rank they later changed to leatherworkers and will not revert, even when all cauldrons in the village are removed and barrels/composters are available.

Notably there are a disproportionate number of novice leatherworkers in the village as a whole.