Experiencing the same problem with one pop bumper on a Jet Spin. Both pops were rebuilt but the one continues to stick, even swapped parts from the good to the bad to eliminate variables. With the ring in the stuck position, I can move the pop bumper body (screws loosened), wafer, etc and it will remain stuck. Like you, I suspect something not quite right with the playfield holes and the under playfield metal bracket that butts up underneath the playfield with holes for the pop bumper ring to go through.

In my case, I know the solenoid is off. I will have to try the demagnetize trick, when I get a chance, to see if that helps.

Finally, had a chance to look into sticking pop on my Jet Spin tonight. Everything on the pop was replaced but the bracket, plunger and coil stop which looked fine after a wipe down. Friend helped me look at it the previous night and he agreed that it appeared to be a magnetic type hold because you could move the body (screws loosened), wafer, etc and it wasn't releasing as if it was binding. He suspected the coil stops if it was anything magnetic. Replaced the coil stops tonight and everything seems normal for the test games I played. Add coil stops to the things to check on a sticking pop?