I just did a race with the ADAC GT Masters 2020 Corvette on Hockenheim using 3x tire wear and a rolling start. The car spawns before the last two corners, and during these corners, you already lose 5-6% of your tire life. I also tested it with normal tire wear, and the tires are still at 99% at the start/finish line there. So it just seems to be a problem with accelerated tire wear.
I can confirm. I also see a difference in tire wear depending on where you are on the grid. 4x: You spawn with 96/98/98/98, a second later there's an immediate drop to 95/96/97/98. By the time you cross S/F line your tire life is: - starting in P1 - 88-93; - starting in P46 - 83-87. 2x: Spawn with 99, a second later you're at 98/99/99/99. Crossing the S/F line: - P1 - 97-98; - P46 - 95-96. Upd: Forgot to mention, it was on Nords 24H.