The spring is too soft. Get a new spring or stretch the old one. Friction between the barrel and point is overwhelming the spring. Hitting the strip produces a light.
Valid touch produces a white light.
Opponent's lame' is not connected. Opponent's body wire is broken. Diagnose by testing at the lame' clip and at the reel wire connection. Opponent's lame' has a dead spot. With some boxes, dead spots can be diagnosed by grounding the fencer's weapon to his suspect lame', and then probing the lame' with the other fencer's weapon.