Villagers change professions for no reason

So my friend started a realm, and I chose to live in a Savanna village, the village kinda died so I started repopulating it, made some of the villagers librarians. Here's where the problem begins, one of them had Looting III as a librarian, neat right? I went to sleep, day time grabbed emeralds and a book to trade with them; I find the villager with the Armorer profession. The lectern wasn't destroyed or anything. A new villager just picked it as job block and the one with Looting picked one of my Blast furnaces. And I can't even turn him back, I destroyed all blocks in my house that he could pick and now he doesn't pick any, not even if I put it beside him.
Update: While writing this, another one switched jobs too, this time to cleric.
update2: while also writing that he changed back to librarian?? I'm so confused