If it makes you feel better, I had the same issues with my GLA mini SS but on a 5lb tank. I also emailed GLA and got no response.
Had to keep the pressure up high (I think 40psi was the same on mine). Otherwise, you could watch the pressure drop over a few minutes.
Set it to 40psi, and it should be fine. Mine has been running that way on my Mr. Aqua 7.5g bowfront for the last 12months on the same 5lb tank. No issues with pressure being constant once set that high. Haven't even had to refill the tank yet (no leaks). Everything seems stable once I got it set.
I was in the same boat as you, would have preferred to run the pressure lower.