Two thoughts..... But I have a problem with both of them
First: Is this a class a B C with a generator that runs on LIQUID propane, has its own shut off valve and line to the tank? or does it run on high pressure vapor (only one outlet on tank but a "T" fitting sends propane to the Generator BEFORE the generator) Or Low Pressure propane (Post Regulator)
Generators suck a LOT of propane. I suspect many regulators can not pass the gas fast enough .. Nothing wrong with the regulator, working as designed, Just not big enough.
Second.. Not all propane is actually propane,, but the difference usually only shows when water gets hard (Turns to ICE hard) if water is still liquid, that's not the problem.