Welcome to the forum.

Make sure both your track and accessory transformers are phased together properly, so that both ground wires are at ground potential, and both hot wires are in phase with each other.

After that, double check all power and controller connections are correct. If that does not solve the problem, disconnect all power and controller wires from the problem switch. Turn up track power, and put a meter or bulb across the "aux in" and "aux gnd" connection and see if you are getting track voltage at these terminals. You should not. If you do, there is an internal short in the switch, and it needs repair/replacement.

Do this suggestion, and report back to the forum.

How many switches do you have on your layout? Do this to all switches.

Larry