Are you saying the bubble rate isn't consistent? Or that it's changing over the course of a full day then resets?
I had an issue with inconsistent bubble rate on my CO2art regulator too, sometimes it would output CO2 at the rate I set it to, other times it would be lower, enough to make a difference in drop checker colour and ultimately giving poor CO2. This was because the working pressure was ever so slightly changing each day. I'm not very mechanically minded, so in all honesty I'm not very familiar with proper regulator practices, but I found advice somewhere online stating that the working pressure can fluctuate if the working pressure dial is increased while the solenoid is switched on. Which is what I had done - initially I found the working pressure dropped a little below where I wanted it, so I increased the working pressure dial whilst the solenoid was on, but this is what led to my issues.
So I resolved my issue by de-gassing the regulator and starting from scratch - setting the working pressure where I wanted it and then only adjusting it while the solenoid is switched off. It's now properly consistent. Sorry if this is super obvious to others, but just thought it might be worth sharing for any other people who aren't mechanically minded like me