In the processing page, while pressing the reset button, you could actually reset the pan / master section but it doesn’t reset the PAN, it works only if you actually move the PAN knob.
Sounds like a bug that needs to be reported to A&H.
This is not a bug and works as intended.
Although pan is displayed on the processing screen for convenience, it is a part of channel routing, and (like send levels) independent for each stereo mix, so should not be reset alongside processing.
As you mention, holding reset and turning the pan rotary will switch between hard left / centre / hard right panning.
Panning will also be reset when resetting a mix by holding reset and pressing a mix key.
Cheers,
Keith.