If it's worked for 2 summers and now it's not, has anything else around your pool area changed since this started happening.
As noted, GFCI breakers are humidity sensitive...also, if it has tripped or been reset multiple times, they can become weaker and trip easier, esp when the season is going from cold to warmer. Does the sun hit this area w the GFCI any? if so, how often per day time of season?
GFCI's are not too expensive. You could replace it w an identical GFCI switch and see what happens. However, since you are still under warranty, I would definitely call the installer and put them under notice of the issue so you can have the problem time-stamped.
Keep us posted and good luck,
tstexx