Potentiometer heats up after changing wiring
The change in wire gauge means more current can flow.  I expect you're getting too much current through the pulse width modulator controllers you linked to.
24AWG wire has a higher resistance per foot than 18AWG wire.  I expect the higher resistance of the 24AWG was keeping the current below the rated current of the controller.  You switched to thicker wire with less resistance, so there's more current going through the LEDs and the controller.  That additional current is making the switching transistor in the controller get hot.