I'm pretty sure it's everywhere I fell around the turn where you have to drift, accidentally fell a bit after the race started, and around the first incline (I played a lot lol but I'm trash) and each time I fell infinitely into the abyss. Each time it felt like I was hitting two colliders that were trying to restart the game and put me back on track. I say that because when I hit these triggers the game would transition to black, like it was loading or something, but when it transitioned back I was definitely still falling. The first trigger is a little after you fall off, the second is a few seconds of falling after that.
I gotta stress that even with these bugs, this is one of the coolest games in the jam for me right now, and I hope you keep working on it. The idea is amazingly solid and super fun.