I still think that OP's problem might be - likely is - the removable valve stem not being tight. I've had the same thing happen, unfortunately recently enough that I should have known better.
It's getting dark, in a hurry to get home, unscrew the valve nut exactly like always and waste a CO2 cartridge in an instant. Likely I unscrewed the valve core when I though it was the nut turning. With a pump, same thing. After I got that situated, air in the tube, I couldn't get the screw-on pump nozzle off without removing the valve core. If I hadn't also had a Presta adapter to just leave on the stem and using the Schrader pump nozzle I'd have been SOL. So I know it can happen that way, and I suspect that's what happened to OP.
Just tightening it down later with pliers wasn't enough BTW.