By using a pressure regulator at the faucet you are also protecting your supply hose.That's strange. I use an external regulator at all times and never experienced that problem. Try borrowing another one for five minutes at your next outing to see if the problem still exists. Perhaps your external regulator is defective.I bought a water pressure safety valve before I learned that there was one in my Airstream already. When I use it, I find that the water pressure in the trailer is severely reduced.
Philip T.