OK- I'm going to make a guess now, then- It looks like you're sanding off a top layer, and you're feathering out the edges. I would guess the problem was putting on a second coat over blush so you didn't get good adhesion, or you had a batch with the mixture off. Maybe- since it was so warm, it had started to kick off before you got it spread so it didn't adhere as well. Definitely call System 3 or send their tech people a photo. but in the meantime... out of curiosity... see if you can slip a utility knife blade under the discolored part and peel it up. The good news is that if this is the problem it's an easy fix. Just sand it off and add more epoxy to your fill coat.

m