Villager's XP bar for trading will sometimes go past the GUI when you, I think, keep trading once they level up, but before the GUI updates with the level up.
Video by [Mod] violine1101 demonstrating the issue: https://youtu.be/Lk7wV0AD19I
Villager experience bar out of gui
Villager experience bar displays incorrectly
Villager trade GUI is bugged
Visual bug with raid boss bar