Don't rule out injectors getting tired. Many brands dont last as long as petrol/diesel injectors.
My last Omega, the injectors were worn after about 40k miles, with the symptom being lumpy idle, partucularly when cold, leading to occasional stalling. In my case, rather than replace injectors, I just had it switching back to petrol under 1200 rpm and not switching back to gas until 1600rpm. Had I known how long we were going to be keeping it for - the lack of LPG in my area made it unviable, but we kept on being able to get LPG on various journeys - I would have replaced the injectors.
The fact that it sounds like yours is over fuelling when pushed, and under fuelling at light loads, that does sound like mapping isn't right, or that the evap isn't getting the heat at lower loads.
In the UK, our LPG is mostly propane with a small amount of butane IIRC, presumably to stop the propane from freezing when cold. I'm guessing this mix was always the same, as I never had to remap mine in that latter years based on time of year.
Yes, I thought they were injectors but something curious happened and I haven't responded until I was sure. After a refueling, suddenly the LTFT went to 0, surprised I wanted to wait for another refueling to see what happens.
Unfortunately, the same problem has reappeared after another refueling, always Repsol at the same station.
The strange thing about this is that you only see the problem if you connect the obd because the car works fine, no jerks and no MIL light