My P-120 was upgraded to 6.0 version and is doing something similar. On start up, the turbine ignites on propane, rpm's increase slightly, then it just runs on propane until I get ACC SLOW and it shuts down. The only way I can get it start and keep running is to shake the propane can really hard. Once I do that, the engine ramps up quickly and runs fine.
I really wish JETCAT USA would tell us what each software version does when they upgrade the ECU's.