Purchased a solar cover last year. Over the last few weeks the top skin of the air bubbles on the back of the solar cover are just falling off. I stopped putting the solar cover on the pool as every time I reeled the cover off dozens and dozens of the back little round skins fell off and I had to spend much time scooping the skins out of the pool. Any idea for the cause? I believe I paid about $120 for the cover.