Only earth your shield at one end only, control end is usually best.
Then disconnect each switch in turn to see if you have a bad one or at least identify which one is playing up.

Don't omit the estop from your test as this also uses the same circuitry.

Worst comes to worst change the reed switches for micro switches even if hanging on the end of the wires.
first thing is to find the culprit............then kill it :lol: