I was concerned that insufficient air pressure/flow could be the problem, but like I said the pressure on the regulator dial seems pretty solid and I can turn the torch arc on and off via the button in Mach 3 even when the G code isn’t controlling it correctly.
If there’s another way to check for satisfactory pressure, I can look into that too one the torch is operational again. I’ll also try doing some manual tests (I’ve used shared/shop plasma cutters before, but I’ve never used this one by hand).