There are a couple possible causes of the problem: contaminated surface before glassing, some sort of epoxy mixing issue, or the black paint caused the epoxy to get hot enough to delaminate while sitting in the sun.

I would fix it by cutting away the blister. Use a utility/razor knife with the blade held almost parallel to the surface to poke through the side of the glass and shave around the perimeter of the blister. Don't cut straight down as it is very hard not to cut completely through the glass into the wood.

Then use a putty knife to try to slide under the edge of the glass to see if more glass has a weak bond to the surface. Don't poke too hard as even well bonded glass my start to peel with enough pressure and a sharp putty knife.

If any more glass peels easily, trim it off as above.

Sand around the perimeter to feather the glass down so the edge is flush with the wood. Make tapered edge at least 1" wide, and sand another 1" or so beyond to remove the paint.

Cut a patch of similar weight cloth slightly larger than the feathered area. Epoxy it down. Fill coat after out to almost the paint. Sand everything smooth, add another fill coat if needed. Sand again.

Re-paint. Maybe use a lighter color.