… Turned out the debris (dip) tube on the valve had clogged with a particle, stopping ALL air flow out of the tank.
I have wondered for years why sintered bronze tubular filters were not available for dip tubes on valves. They could have a lot more surface area than those on a first stage regulator, and would ideally be a little finer. I would pay extra for the option. Say something ~¾” OD x 2” long on the end of a 3” dip tube.