I believe in most cases it is in actual fact the under documented case of the drop target spring screw coming loose. I had similar issues tried different stuff with the plastic ledge which seemEd to help a bit for a while, but found a guy mentioned the screw on pinside - sure enough I checked and it was loose! Tightened it up and never had an issue since. I think people are too quick to mess with the ledge and should always check this first