I've noticed during my dramas withe intank fuel pump that if I try to run it without submerging the pump pickup in petrol it sucks in air and subsequent submerging in petrol won't work(it won't pump petrol) even though I can hear the pump running. The way to overcome that was to stop the pump running and start again(disconnect the power to the pump and reconnect it). This was while having the pump on a bench with a small petrol container to produce the conditions inside the tank.
I'm not certain whether this is a pump fault or not, but I suspect it is, 'cos when the tank run out of petrol the pump does get filled with air through the breather(s) so the same condition can produce the same result. Turning the ignition off and turning on again can mimic the scenario of power disconnect/connect. My overall guess was that the pump was faulty so I wired up a cheaper external pump while still having the internal pump & it's plumbing(sealed but left alone in case I wanna swap over the external pump plumbing lines to the internal pump). I opted to not to purchase a new internal pump 'cos I wasn't sure(still not sure) whether the pump is faulty or not(internal pump is around $150 and I didn't wanna spend that much money without confirming it). External pump setup was super cheap and effective, but I will have to get back to the internal pump issue sometime in the future.

I think the internal pump is indeed faulty in my case 'cos when the vehicle in on LPG(I run it on LPG all the time) the intank petrol pump still runs all the time, and there is no petrol in the petrol tank most of the time. I reckon it's been pumping air(pumping dry) for too long and that might have partially stuffed it up. The wiring by the LPG guy was bad to make it run all the time I reckon.
I have corrected that issue by rewiring so the petrol pump doesn't run anymore while the engine's running on LPG.