Use superglue on the delaminating areas, and use plastic wrap to press it down.

For the cracks in the glass, there was a similar discussion here:

https://pinside.com/pinball/forum/topic/help-how-do-i-save-this-fireball-backglass

Once you address the cracks, then I would use triple thick.

I've used it on over a dozen backglasses from various eras and haven't had a problem with it yet. Maybe there was something on the surface of that particular backglass? Or did you use something other than the krylon brand of triple thick?

The glue won't be visible--it's completely transparent. If the delaminated paint isn't pressed down all the way, then you'll see air pockets. But, you can address those with a needle and super glue if necessary.

Make sure you get the 15 second liquid super glue, not gel or 5 second glue.

I've used the superglue technique several times to save delaminating backglasses. The thing about delamination is that you need something between the glass and the paint. Spraying triple thick on the back side doesn't do much to adhere it to the glass.

First, prepare a piece of plastic wrap enough to cover well beyond the area you're gluing. Make sure it's as flat as possible, and set it aside. Then put generous amounts of superglue under the area that is delaminating. Take the plastic wrap, cover the area, and gently press down (be careful not to break off sections/flakes of paint when you do this. Hold it for about a full minute then let go. Leave the plastic wrap on there for 24 hours, then remove it.