Probably you run out of food and die. 

Oh I think I know what happens, when you hit object it disappears but it is quite obviously that you hit object because it is visible before you hit it. I am sorry if that confused you. If neither of this cases are not true, I would appreciated to you tell me more about it. 

You might be running in to the "Walk" sign that's by road crossings. It's hard to tell sometimes if that's an obstacle.

Thank you on review!