Since I updated, Villagers that I haven't locked by trading with them at least once, are changing their trades during workhours.
What I expected to happen was...:
I have a trading hall and I remove and replace the workstation of said villager to get a trade I need. I found a good trade and I went to get some emeralds so I could trade to lock him.
What actually happened was...:
When I was back, his trades have changed, and so did the other unlocked villagers.
I have observed that this happens only during work hours, so I assume they are losing their profesisons over and over, until you lock the trades.