I took it apart and did the usual rubbing alcohol cleaning. I also turned off the main tank but left the regulator open, when I took it apart what ever gas is still in the regulator rushes out. I did this twice to flush out any debris.
I have also stretched the spring (carefully), to ensure it's fully extending when inside. I decided to use a queue tip with minute amount of olive oil to put around the top of the piston. not even enough to be visible afterwards.
I reassembled everything and did about 6 test start and stops by plugging in the solenoid. Everything was working well after this. I've been here before.... I can only assume I get more debris and the problem repeats or the solenoid spring is catching and not fully extending back up to block CO2.
I have my output side pressure set to about 12 psi, my thinking is higher pressure output makes it harder for the spring to shut off the flow. Not sure if this is a correct assumption but it makes sense.
I will montior tomorrow and see how it performs. My ph controller often toggles power on and off near the end of the day when my PH get's dialed in at 6.1.