Basically it changes from ABS default to weak when you enter the race, when qualifying starts or when the race starts, check member list when you enter the race and you will see if you have ABS weak or default (watch Herimopps stream at 5:43 to see three people having it before the race, but I think it changes when qualifying and/or the race starts). Seems to only affect lobby racing but I haven't driven enough Sport mode to know for sure.
Changing your ABS to off and driving to first sector and then changing back seems to fix it but I forgot when the restart happened. Race pace wasn't affected much since I don't really trailbrake during race to save tires, only places where I lost time was the "chicane" in the mountain and the following turns before the long straights were I had to be very careful with the brakes. However tire wear is worse since the tires slide more during braking. My two crashes weren't caused by the bug but I'm willing to test out different methods for preventing the bug.
If anyone wants to experiment in a lobby, tag me on here and I'll help out, you can't really do it on your own since you can't start the race.