Sounds like that's what happened to my high-level fletcher. Very annoying. Seems like we need to lock them up (like I have done with my mending book librarian 😃 )
I have also noticed this. This prevents the original more qualified villager from restocking. I added more blocks of the appropriate type near the problem villager and that helped but because of the above issue, this just multiplies the problem if your village is growing.
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I also had a high level villager apparently despawn, presumably because of this.
Still seeing this 1.15.2. Very reproducible on opening chest in sunken ship. Have upped the max-tick-allowed to 480000 and still crashes.
This dude actually turned up in a house far away from the village center and his (or what was originally his) block. The villager who took his block ran in front of me while I was taking aim at a creeper and died a fiery and unloved death so I guess there was at least some karma there.