I had a similar problem: everytime i fight a zombie, the screen turn black, dying obviously, and restarting every single time

I closed the game on xbox one and i've lost EVERYTHING, 10 or more hours of game. I thought i was dead because i was near to some zombies, but when my friend try to search for my inventory, found nothing. So i don't think i'm dead, but i've just lost everything, and now.. if it's possible, i want all back