My act 2 mercenary always had a full experience bar. On mouseover the numbers were shown correctly (something like 9.585.946/10.246.500). It seems that only the display was bugged. Although he leveled up a few times it still was bugged. Restart the game didn’t fix it either.
So i bought a new one and it worked correct again. I have a screenshot available if needed.
Yeah my merc has the same experience bar bug. Purely cosmetic as the actual numbers don’t reflect this.
Edit: It might have something to do with the fact that the merc is at the same level as my character. If it gains anymore xp they’ll out level me, so it’s xp and xp bar remains static (almost full)
I have the same issue and my merc is 10 levels under me so that’s definitely not the issue.