The gas valve turns off for no apparent reason and the lights blink on board for (alternate) 'watchboard code'

If your furnace is equipped with a circuit board it controls most if not all of the system inner workings. As such it more than likely has a light or two that will flash or blink a code to try and tell the service person where the problem might exist. Usually located on the back side of the furnace blower access door there will be a diagram that explains what the blinks/flashes/codes mean along with a wiring diagram of the unit.