Trouble with gas pressure

So I have the 17” blackstone which, from the factory comes with a setup intended for small portable propane bottles. I purchased an adapter intended for a standard grill propane tank. Initially it worked very well but after a season or two, I’m experiencing trouble. I’ll start the grill and the flames are blue and high when on high. After maybe 20 minutes, the flame drops considerably to where it’s maybe 1/4 of the intensity of when it started. Flame remains blue even when very small. I’m confused as to what is happening. Is there a proper orientation for the regulator (upside down or no?)? Is it possible the regulator is freezing up inside and reducing flow? Any recommendations would be appreciated.