It sounds to me as though there is a restriction of some kind in the gas pipe or
regulator itself. The device lights u0p OK, but when the pressure in the pipe falls because of restricted gas flow, the device has insufficient gas to remain alight and it flutters or goes out. By the time one has gotten it re-ignited, the pressure in the pipes has built up again--but because these burners use a lot of gas as compared to an ordinary burner, the pressure in the pipes soon falls and the process is repeated.
I think you should replace the
regulator with a larger one, if simply disconnecting and blowing through the pipes and checking for dings and blockages fails to find any faults or blockages.