First: The heat pumps simply will not work below about 40 degrees F. They are designed to work as a heat source above 45 degrees F.
Second: We had the same issue with our 2015 30' FC. Furnace would kick on correctly, light up fine and then the propane would shut off. It would recycle itself between 5-7 times and then finally kick on and stay on. Everything in the system was replaced except the propane valve within the furnace and the sail switch, including the valve at the tanks.
With all this done it worked at the shop, but I went to storage the next day and it went through the cycle again. So I took it back to the shop and this time they replaced the valve in the furnace that controls the propane flow - it worked.
I've tested it periodically at 15 degrees F and then yesterday at 28 degrees F and both times it fired the first time, stayed on until the chamber got too hot, kicked off which it is supposed to do, then came back on and stayed on until trailer was warmed up to 70 degrees F.
So, long story shortened - you might have them check that valve. As our main board was replaced, igniter was replaced, tank valve was replaced. OUR yours could be as simple as the sail switch which others with 2014 - 2015 have had issues with.
Ours was all done under warranty. We also carry two small ceramic heaters all the time and always have, just in case.
2020 28' Twin Flying Cloud-(Our 5th Airstream)
USAF Master Training Instructor (TI) - 68-72