If your solenoid is not fully closing the flow, probably the dirt from the CO2 cylinder stuck inside the orifice or on top of the plunger. In such a situation when the solenoid is in OFF position the dirt will prevent the plunger from closing the gas flow completely and you will still see some bubbles in the bubble counter.
To clean the solenoid, please follow the DIY steps from the tutorial below.
Disconnect regulator from the cylinder,
Release all gas from the regulator (both gauges on 0)
Remove the electric coil from the solenoid
Step 3 (Solenoid version with two screws)
Unscrew two small screws from the bottom of the solenoid body
Step 3 (Solenoid version with 13mm plunger housing)
The Pro-Elite and some Pro-SE units require 13mm wrench to remove the plunger housing
(A) - Orifice
(B) - Plunger
(C) - Spring
Inside the solenoid, you will find spring (C) attached to the plunger (B), please make sure rubber part at the end plunger is clean and flat
Check the orifice(A) if it is not blocked with dirt or small debris
Stretch the spring(C) so it will be around 0.5cm longer
Assemble all parts back together, make sure all connections are tight as originally.
Check for leaks with soapy water.