I had a similar issue on my last one. After the first few runs, I realized I wasn't plugging the quick connect in all the way. Since yours WAS working better, I'd suspect either the connection getting stiff or obstructed or, as nelsonc said, something gunked up in the burner (probably the most likely).
2015 Chevy Silverado LTZ - HD tow package
2017 Rockwood 2703WS Emerald Edition