Different top speeds at different refresh rates (pc) bug

I encountered a very weird bug, i found out that when i play on 4k 120hz, the top speed is lower, where it is higher at 60hz.
I did the same short custom route multiple times with the sesto elemento FE, and with 60hz i hit 320kph, and with 120hz no more than 302kph. At 60hz the results screen also takes a little longer to load.
What is happening here? Added info: i use vsync and gsync, with a rtx 3080, no motion blur, and everything else is on extreme, except deformable terrain quality, this is turned down 1 step.

I did not read the piece about submitting a ticket first, so i did that now anyway, but if someone here has an answer, it would be fine too… Anybody else noticed this problem? I only switched back to 60fps because i was monitoring my temperatures, and wanted to check the difference.