You might be better off contacting GMG directly.
In the meantime; If the grill is in the shade and you turn it on, does the control read ambient temperature or close to it?
Does a food probe placed in the pit near or attached to the RTD, read the same or close to it as the pit temperature - with the pit operating? If the food probe is close and the RTD (pit temp) is off, the
problem lies in the RTD circuit, most likely the RTD itself.
I am interested in what your problem ends up being. It isn't COVID-BBQ.