Quoted from Magicmike0:
Mine did this too. It ended up being the L bracket on the back side of the guide rail(above the flipper) was broken. The one that secured the rail to the playfield.
My guide rail was no longer guiding the ball down the flipper anymore, as it was sitting back too far. I still haven’t fixed it. I ended up putting an old flipper rubber between the post(that sits behind the guide rail) and the guide rail.
It works for now. I haven’t had any issues except it vibrated loose once. I put it back and have played several games with no problems. I have contacted Steve from the pinball Resource and he didn’t have any guide rail replacements.
Maybe check to see if that’s your issue? Hope it helps.
My L bracket there was also broken. I ended up sticking a small plastic post there instead for the guide to rest against