Consider this a bump.

I have the same problem. We resurfaced the pool in June and the first rust stains did not appear until 3 weeks later. New plaster - now with rust stains. The light was, of course, pulled for the resurfacing. I replaced the light seal after pool was filled, when the GFIC kept tripping and we saw water behind the glass.

We didn't replace the light. I'm beginning to wonder if the heavy acid demand of a new pool might be causing the back of the face plate or other components to rust. I'll pull the light soon to explore, but dread it. In the meantime, anyone know how to get rid of nasty rust stains around light niches? Or what might be causing the issue?