In the fight with the undead in the dark crypt, I had cast the light spell on three of my part members. To my eyes, everything was lit up quite nicely however when you hover the mouse over one of the undead, it said I would be attacking with disadvantage, even though the target was surrounded by characters with lit up weapons. I didn't check the actual roll to see if it said disadvantage, so perhaps its just the % hit predictor that's bugged.
