Good Morning.
Propane tanks as you know have a regulator for safety and also designed for regulated pressure. Some of the regulators on in line and some are right off the top of the tank. What the regulator is like a diaphragm, it allows pressure from tank to go through to your device you are operating. Its kind of like a thermostat on a car that opens and closes with temperature as demand calls for it. Difference is the propane regulator is designed for pressure at a regulated psi (pressure per square inch) So, maybe replace regulator..

BUT before we do that, here is my logic. Sense you said it has automatic igniter and won't light, a person would think, well maybe the flint electronic lighter might be worn out and needs replacing. I am not convinced on that, BECAUSE, you said you tried to light it with a match, but still wont light. As you know, the electronic ignition lighter is made to spark and light so a person does not have to use a match. Now, that being said, if it was getting gas, it should of lit right up. So, now it tells me it is only in two areas the problem of not lighting. The propane regulator, or the main gas line going to the igniter. So, if you can follow me on this, i will try and explain what to do.

Where the gas would normally come out if igniter was working, i am sure has some tubes, small pipes, port holes, etc... What you need to do is get a sewing needle, or something of that sort and try and poke (clean) holes.( DO NOT use tooth pick as if breaks off in ports or holes, will cause more blockage)

Here is my point, you either have a bad regulator, even though you have fresh tank of propane, but the regulator if not working right, will not propane to get through, OR you have the tubes, ports that come into the unit or carbon up to the point of blockage for propane to flow.

ANOTHER NOTE: sense you said it does eventually light with a match after a long time, but then on runs on low for a few minutes then shuts off. This tells me there is a restriction or possible blockage. Again, this could be cause from regulator, or tubes that flow the propane by the ignition. Think of it like a barbeque, that get cakes up from cooking on the grill, needs to be cleaned.

I hope this helps, if this helped please respond with proper rating, and feel free to contact me for additional information that i possibly could help you with. Thanks Mike