Your problem IS noise and no supressing or removing the supervisor is going to cure that.

the "How can I resolve noise problems?" entry in the FAQ gives you a list of things to do.

Approach this systematically, not "try this, see if it works".

1) remove possible ground loops (if the contactor return goes to control PCB ground, get if off there)

2) RF isolate (ferrites) the wires to the contactor driver (which should NOT be on your control PCB)

3) do the first 5 steps in the FAQ and test, if no success do them all.

Erik