I'm having the same issue with an older 5-gallon. A very slow leak at the PRV discovered by spraying StarSan on it. I applied some keg lube to the tapered seal at the bottom of the PRV and I'm testing it now under pressure. If that doesn't fix it, I may put some teflon tape on the threads of the valve.
Good Temp Control -----> Happy Yeast ------> Tasty Brew