Do you always run the car on minimum petrol because it’s LPG? If so that’s what your problem is. If the tank is never filled up the resistance windings on the sender get corrosion on them and go open circuit.
I’ve had this happen on my old VE SV6 before when I used to just “splash and dash” constantly. When I needed to go on a long trip and filed the tank the gauge didn’t work and the dash said contact dealer.
I put two and two together and after filling the tank up a few more times the gauge went back to working properly and now I make sure to regularly fill my car with petrol and run it on petrol at least one day a week to keep the petrol turning over.
