I guess your character moves down on a steep until it gets to kill z area of the world. which you can change from world settings .
or maybe you set your character life time span. make sure that is zero
you are welcome.
i promoted my comment to an answer which you can mark as resolved if you like
hi all
i have a problem with my game. when i play my lvl after my player run a while the game stops on it self ?
i have tried google to find any similar problem but no luck so if some one can help i really appreciate.
thanks in advance 
thank you so much dear “saeedc” you answer did helped me a lot. it was Kill Z problem i just change it to match my map and it works fine.
thank you so much.