Oh no need to apologize. I had actually searched on pinside for threads about clearcoating backglasses yesterday before spraying, but I didn't find yours at that time.
When did you start to notice it cracking like that? Mine has been drying for the last 17 hours or so, and it still looks quite smooth, with no new defects or cracking (yet at least). I read that I should leave it for 48 hours though, so it still has a ways to go. My spraying technique was a bit different than yours, so we shall see if that makes a difference. If I read correctly, you did a few thin layers a few minutes apart. I did a light spray first, waited 30 minutes, then a heavier spray, waited 30 minutes, and then another heavier spray. I had a few areas where the art was curling up, so I wanted to put a heavy enough clearcoat on to hopefully press it back down. I'm also using seran wrap and small wood blocks to flatten to raised spots. I'm most nervous about how well the seran wrap will pull off when the clearcoat has dried.
I'm currently running a dehumidifier in the same room as the backglass, to maybe help the drying process a bit.
I'll keep you posted on if mine cracks like yours. Sorry to hear/see that happen to you.