I have a PRO-SE series and noticed today that the working pressure gauge reads 0 and the high pressure gauge still reads ~800 PSI. Turning front knob is not changing working pressure

I’m afraid dirt from the CO2 tank has stuck inside the regulator’s 1st stage.

Please follow steps to fix this issue:

remove the regulator from the cylinder
release all gas from the regulator so both gauges are on 0.
remove the CO2Art logo sticker from the back of the regulator
unscrew the bolt from the back with a large screwdriver
please, clean internal side of the regulator and make sure that there is no dirt on the bolt side
assemble all back together and test it.