That one's a mystery. Sounds like blush, but it seems like you did everything you should to avoid any blushing problems. What kind of epoxy and what kind of hardener did you use?

I checked the data sheet on Goldspar (through Interlux's web) and they don't recommend applying it if the ambient temp is below 40 degrees. But you had the product on for a week before the temp dropped that mark. It doesn't seem like the temp a week later should have been a problem. I'd suggest contacting Interlux if you have the time. I couldn't find any contact numbers on the website. The only option seems to be to ask via email. I did that once a year or two ago and got a reasonably helpful response, as I recall. But I think it took several days to get it.