Yeah, guys, I figured it wasn't blush because it is Maas, and, if it did blush, wouldn't it be all over, rather than a spot?

It was less than 1 day, and sanded (because I had some thicker areas where I was about to glass; then extended epoxy beyond the glass).

2 ideas, as I've been thinking. What if the epoxy ratios were off, slightly? Or, maybe it's my re-used cotton rags. They've been washed, but could be leaching out some old contaminant?

: Maas slow shouldn't be blushing. I think 72 hours is too long. Are
: you letting the previous coat cure too long before overcoating
: perhaps? Liquid on very dry is maybe causing a meniscus? Any
: slight contaminant or even bit of dust can cause the surface
: tension to relax in a tiny area if the layer below is very
: smooth and hard. Try to evenly cover a sheet of glass with a
: film of water.

: Working in a heated space with a mask on. Is it possible you are
: dropping the occasional drop of perspiration on the paddle or
: boat? This dries and leaves oil or salt behind.

: Et