there is a bug that all players get erased, this happens when u close the app when it's saving or loading, this also happens when u play for like 2 hours or more and the game close by himself and this can happen saving or loading... to prevent this from happening i save every 8 or 10 games, close the app and start again.
other way to get ur save f*cked is getting too much money, if u get more than 2 Billion ur game numbers gonna go negative, them ur club finances gonna crash, this happened with me after i got in premier league, and every season the board would fire some of my staff and put almost all my players in transfer...
note that this bugs may have been fixed, but i doubt at this point.