Today when trading with my Cartographer villagers I noticed that it will freeze my game when leveled up a rank (any rank). It's frozen like my player can move, but all mobs are frozen, broken blocks don't drop anything etc. This can be replicated by trading with a cartographer villager until it is leveled up a rank. This freeze can last anywhere from 2 - 30 minutes. If you try to exit the world, it will never get out of the "saving world" screen. The only way to close Minecraft from there is task manager.

This did not happen with any other villagers I traded with, just the cartographer.