I have potent robe texture glitch too, but on Gale. If the camera is far away it goes blank/grey. When I get close with the camera it appears again.
Interesting... I hadn't tested Gale since I always have either Wyll or Gale in my party - never both.
Horns/skin color aside, both Gale and Wyll are human males with the "small" body-type - so perhaps that's what's causing this?
I suppose I could go back to a save-game of my previous Tav who was a small body-type human male to test this. Since he was a Bard, I never used the Potent Robe on him during his play-through.
S.
