I'm also having this issue. Doesn't happen right away though. The door works 100% perfect for about 45 mins and then it starts getting weak. I upgraded to the stronger coil and the door definitely opens up quickly, but after awhile it sags. I'm hoping it's cause i didn't solder it perfectly. It was a pain trying to balance the coil, wire, diode, solder and gun at the same time. The solder seems ok, but ya never know. I'm gonna have a friend help hold it while i solder it, hopefully that solves the issue. I had the garage door sag with a ball trapped behind it, happened late in a very long game and i had to watch the timer run out

hmm, the thing that pushes the door open doesn't seem flattened or worn in any way, and i have the stronger coil installed, hoping it's just a bad solder job, i'm not sure yet.

I had a decent game earlier "78 million" and it started happening towards the end of the game, i did manage to use the trick by holding the ball on the flipper and pressing the other flipper to re-open the door. That seemed to have worked, but it was tough to do when i was in multiball. I would have ended up with a higher score if the door wouldn't have started messing up near the end. My current high score is 95 million.

I love this game, i'm so happy i bought it.