I experienced this exact same situation! Here is what I was told the first time... "You slugged your tank, you turned your tank on too fast and the regulator reduced flow thinking it was a leak, turn your tanks on slowly."
Next camping trip furnace worked on day one, then no go. Tried an experiment, turned stove on, burners working fine, turned furnace on, stove flame goes to almost nothing. Turned all gas apps off and furnace fires up! Then ok to use other gas apps. Took trailer back to dealer for unrelated service and told them, here's what they said..."Bad regulator." So, hopefully when I get the trailer back I will have a thermal blast like the surface of the sun.