I have played around about 40 hours of this game, and have died countless times to this seemingly random bug. When playing the game, have you jumped on a slope or side of a random object and randomly just died. Well I have believe that I have found what the issue is;
When your character is at the very edge of a flat object such as a wall, the character acts like it is falling. If the character moves forward keeping to that edge, their momentum will be pushed forward and gradually gain speed until reaching the max falling speed.
When your character is on a slope which is above a 45 degree angle, this can also happen as seen in the video.
When your character jumps on a railing on stairs inside a building, you have the possibility of dying because the angle is placed in such a way that you instantly go to the max falling speed.
Bin bags or junk also seem to make this collision momentum glitch work too.
If you want to speed run this game, I'd say practice this on lots of different objects and railings as you can go from running speed to faster than a car speed in a small amount of time.