Perhaps your game is missing the round plastic above the stand up targets? I’ve never had this happen on my game. Here’s a shot of mine for reference.
If it’s there then perhaps your flipper rubbers are sitting too low and causing air balls... could be something on the playfield as well. Misaligned target etc... try and pay attention to what the ball hits next time it happens. Or have somebody film a game in slow motion until it happens. That should help you narrow down the culprit. Good luck!
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