According to JBL support - that hole is the relief valve. In my opinion, it's not the relief valve, it's a hole in the threaded body of the regulator housing that serves an unknown purpose and the actual relief valve is the larger black piece of plastic that can be removed and has a spring underneath it to vent excessive pressure?
They have said According to the description, it will be a defective internal seal that must be replaced, this solution you describe is not good. Please replace the gasket.
My solution was adding PTFE tape to the threads of the knurled locking nut to block the random hole in the body that seemingly serves no purpose. The regulator is now holding pressure and seemingly works fine?