Matt
I didn't have 120 litres. For the first japan race I had 21 and for Europe I had 23. Some people who overtook me were on harder tyres and had more fuel onboard.
Me and a few other people in my league have had similar issues, losing as much as 15 positions on lap 1 to people with slower drivers, cars, tires, and more fuel. On one or two occasions even to people who didn't make a strategy or setup. I raced at Hungary today and lost 9 positions, on pl5 for most of the lap but without overheating tires. I was losing out to people who should be slower in terms of car and driver, and they were all within 2 laps of fuel. It's far too random.