World rolls back after exiting game

So I will be playing on a minecraft world, I will click save and quit and then stop the app from running, but when I go back to my world, say a few hours later, about 30 minutes of progress is gone and it rolls back to a previous point in time. This has happened on multiple different worlds, and even when playing with friends via wifi. This happens almost every time I log on to my world. Help will be appreciated!