Villagers profession level does not update correctly

The bug

Trading with villagers does not update their profession level correctly.
This seems to be completely random, it can be stuck at any profession level.

How to reproduce

1. Summon an Armorer villager.

   /summon minecraft:villager ~ ~1 ~ {VillagerData:{profession:"armorer","type":"plains"}}
   

2. Try to unlock his next profession level.
   → Around 1/3 of the time, it won't unlock it next profession level