I also had this and I agree with you that it is a deterioration of the epoxy. There was no blush and no de-lamination. After a year of two of use the epoxy over the glass just seemed to disappear. The boat was stored in a closed boathouse (out of direct sun). I had not put on enough fill coats or any varnish on the inside, hoping to keep a slightly rough surface to prevent wet bare feet slipping. I now use three fill coats and lots of varnish on the inside. I have not had a problem since I started varnishing the insides. It is not quite as white as the photo shows, but still obvious.

John

: What causes this and what is the best way to fix? I know there have
: been discussions on this before. This boat is stored in a barn
: with a cockpit cover on it. It is used primarily in a fresh
: water pond for rolling. The okume was sealed and then the glass
: put on. In the fillet area, the fillet was put on and the glass
: put over it while wet. I looked down into the foot area and
: there are patches there too. It was also painted with urethane
: for protection.