Sad to say but mine is going the same way after about 18 months. Stored outside but seems to have come on suddenly with the recent warm weather. It's probably down to keeping it in gel coat for so long before having it painted. I can't see me getting anything done about it this year so when the time comes may try to provoke it with a bit of gentle localised heat. It will be interesting to see if anything happens to the doors. If not, then my "damp" grp theory is probably the most likely reason.
I had similar happen after flatting primer with wet & dry (used wet). Since that problem I've always used the W&D dry - it's not as effective and needs brushing or replacing frequently but I haven't had it happen again. Maybe a coincidence, but I suspect it takes several days of hot sun / dry conditions to dry before putting on top coat if wet flatting is used?