ABS ate my Borosilcate !

There's an inch long meandering divot in the surface of my 1/4" glass plate and the mating chunk is adhered to the ABS piece I was making. What the heck? How often does this happen? I had been thinking of the glass plate as indestructible, unless I dropped it or did something else clumsy or stupid. I guess not. Now there's this little ersatz dry riverbed thingy in the middle of an otherwise pristine surface. Might as well be the grand canyon.

Yeah, I know you're thinking "Hey, just flip it over, it's only 50% gone". Not so fast, I'm a Maghold user. It's payback time for all those seconds saved not having to deal with clips or pads etc.. I get to discover how easy it is to separate that steel plate from the back of the glass. It's only stuck on there with 60 square inches of 3M 468 MP high-temperature sheet adhesive. I don't know if hi-temp is going to be the answer for getting it to loosen, but I guess I will find out. I'm thinking of that video cncartist did of scraping Qidi blue BuildTak off the metal build plate...

And then I get to flip it over and re-apply it! Any suggestions? What causes these divots to happen in the glass? Anyone else have this happen?