Most likely dave is right. Piece of trash stuck in the valve. Might have had something in the fill adapter go unnoticed which went inside the tank then got caught in the valve seat while firing. refill and try again and hopefully wont give any future problems. (check fill adapter for debris before refilling).
I’ve heard it can happen if a pellet isn’t fully seated, not sure why that should be. Only other thing that comes to mind is a piece of trash caught up in the valve. It might be self clearing, or you might have to pull the valve and take it apart. But I’m just guessing, and if it’s a bad guess, I’m sure someone will let us know :-)! Good luck.
Most likely dave is right. Piece of trash stuck in the valve. Might have had something in the fill adapter go unnoticed which went inside the tank then got caught in the valve seat while firing. refill and try again and hopefully wont give any future problems. (check fill adapter for debris before refilling).