Had same issues in twice in my 5th wheel. First time it was the connecting hose going across the trailer, from driver side to passenger side where the regulator is.
Further to what Herk7769 states is a very common problem. The regulators have a tendency to stick when they get older/and or sit for a long time.
Most of the time with the regulator this is what I do: Turn off propane, release pressure by turning on the stove.... let sit for a minute or so, then turn stove to off position.
Now turn on the gas very, very, very slowly and see if that works. If you hear a strong click or thump you may have to repeat the procedure.
That the regulator sticks is also very common on home BBQ's, happened to me lots with the old BBQ. My daughter inlaw had the same problem just two days ago and the above worked just fine. Good luck.
Cortes Island, BC. Canada
Pony: 2008 Dodge 3500 Laramie, 4x4, Quad Cab
Harness: Hijacker 24-AS-18 Autoslide, Demco Glide Ride Pin Box
Chuckwagon: 2011 Rockwood 8265WS