Decided to start a fresh character and after clearing a few dungeons after the Luxury and Mystery Merchants were unlocked it was not updating the counts of kills for Powerful Mobs or Enchanted Mobs.  I even kept count of last dungeon to see if it was a fluke.  Killed 9 Enchanted Mobs but Mystery Merchant still says 0/5 for 3rd slot.  And killed 2 Redstone Golems and Luxury Merchant still says 0/10 for 2nd slot.  I even attempted to get last hits via melee, ranged, and artifact.  But none registered a kill at appropriate merchants.