It's the regulators. I have a set in a keezer that move all over the place. Strike that - They don't. When I move the screw it takes up to a day for the needle to point where it's really set at. I don't know why. My other regs don't do that, but these do.
Set it for 12 and a day later it's at 18. Crank it back down to 12 and a day later it's 8. Eyeball it somewhere in the middle and a day later it's at 12
You'll figure it out with practice.