villager trades are switching

Any time i trade with a villager after some time another villager steels the first villagers' job example: i grind for mending village two minutes later I have two librarians one lectern and the mending villager won't refresh his trades also i have a bug where the mending villager no longer sells mending books there a picture of a mending book but when you buy it he just gives you his other trade of bookshelves plz fix