Summary of the bug : Once in a while a respawn can kick the game into slow-motion, the cars, gravity, clock, etc. advance at about 1/8th the normal speed. It has only done it when respawning after falling off the track on Skytrack and Acrophobia, and I believe it happened once on Transport. Restarting the race from the pause menu fixes the problem.
On which speed did that happen (if related to physics) : It has happened on both High and Low
Your specs : AMD A10-6800K, R7-265 (a.k.a. HD-7850), 24GB DDR3 @ 2133MHz, Win 10 Pro 64
It may or may not be more likely to occur while holding certain buttons on the controller, but I am not sure of that.