This is a common problem. When I worked in the lab at Bally we actually purchased a crude Polaroid Polavision 8mm camera system to study the problem. Under super slow-mo we discovered the target would bend backwards into the rubber and bounce back into position before the spring could pull it down.
The fix is to use thinner rubber behind the target and/or double up on or use stronger springs.
Or go with what the game design team did back then, change your slogan to, 'That's not a bug, it's a feature!'