I've bought a star wars X wing play at. I've used it twice, I've always stored it horizontally inside and it's starting to bubble or develop bubbles in it. Has anyone seen this and is there a way to fix it?

Is it exposed to heat? For example, left in your car, above the exhaust fan in your kitchen, etc?

I bought my playmat from FFG the day they announced them, so I've had it a long time and I store it in my hot garage.... still never had any problems with either of them (I have Death star and starfield)