Hi 
I play the game from PC
This graphics bug occurs when using Sacrifices spell Arcane Surge to kill last ally, and Princes Elspeths Royal Demand to summon a random knight. Sometimes a yellow effect graphic is left on top of the summoned knights card. Thats the indicator that the graphics got bugged and when that knight is Arcane Surged the card that was there originally is displayed but without any effects to the game … so it’s just a “ghost” of a card. I do have a video about it too. But heres a picture.
