Well, this is not good...
I am hitting the same bug, and my completion rate is 45% at this point. My last autosave is already having the bug, and my last manual save before this is at 33% ("the kickstand"). If I have to replay it from 33% it would easily cost me another 30-60 minutes. And the mine road racing is an unnecessarily and unexpectedly boring and drawn-out section I'd really not like to repeat, especially with the cave finding after that (a lap along the mine road takes four minutes IRL, and if you miss the two second window you apparently have to do another full lap!) And you can't do manual save while riding the road, so every time I would hit this bug, I would have to do that entire thing again.
And then I don't know what to do with the ramp. (Although I might google a walkthrough.)
Did any solution for this come up over the past 2 years?