[Lonestar38ZRC]

If the switch works at the generator, there is nothing wrong with the controller.

I’m pretty sure you have a GTSS (ground to start, ground to stop, three wire system).
The center terminal on the switch is ground.  Either of the other two are start and stop, they need to touch ground.

So, do what Jack suggested and check the back side of the switch.  While you are there, take the start wire off of the switch and ground it.  If the set starts then the switch needs replaced.

Richard asked if the other switches operate.  If they start the set with no issue then it is likely the switch.  I have seen the wires separate between switches (dash to kitchen).

Edit:  since you state both inside switches have the same issue then the ground to start wire is not connected to the controller.  Check the wiring from the fixed point inside the generator box to the six pin molex style connector on the back of the Kohler panel.   You have not stated which brand you have, I’m guessing it is a Kohler.  Check the continuity of the three wire circuit from dash switch to generator.

Generator is a 20KW Powertech 
I will check the ground to stop/start inside the controller.  The main thing that confuses me is the sporadic nature of the issue. At times it works great. Other times it won’t engage the start circuit.