I restored a BK2K and cleared over the waterslide decals with excellent results. I cleared the playfield with several coats. Wet sanded flat, installed decals, then buried then in more clear. You can't even tell they are decals unless you really look hard

Ouch that's not good. What was your prep procedure? Did you mist first coats? Sys 11's are are very tricky and risky to auto clear.

So many things can go wrong. Your guess will prob be as good as anyone's . The sanding sponge could have had something on it. The playfield prep might not have removed all the oils. I mist first with a snap dry clear and try to spray when its warm and humidity is lower than 50%. I'm no expert but on the only sys 11 playfield I cleared I sprayed a few coats of Varathane first to seal it then weeks later cleared with auto clear.

https://pinside.com/pinball/forum/topic/system-11-inserts-clear-coat

Wow that's aggressive 100 grit. Obviously if you go thru that clear and into the art work is probably going to be firewood. I wonder if you can rough up the bad areas, brush some 2PAC to try and level before you hit it with sander?

Curing idea I've used when cold. I take play field inside house to a heated bathroom, turn on exhaust fan, close door, put sign on door to stay the F out