not saving

Sometimes when I exit the game and return later on i will find that much of my stuff has gone missing from my chests or hands. the first time i noticed it was in survival mode when a healing potion in my chest was gone after i closed the game again. The most recent one was today when i closed it at about 11:00 in the morning and started it back up at 1:00. My 47 iron ignots, 12 gold ignots, 27 red stone, and a diamond went missing along with my iron sword, my iron pickaxe, my flint and steel and 4 mutton.