World doesn't auto save at all while actively playing for 2 hours.

I had been playing on my Kindle Fire hdx 3rd generation for two hours, when it suddenly died, When I went on the world later, all of the progress was lost. Before the most recent update, It would always autosave frequently. I do not understand why it isn't now. Part of the problem may be that I was playing in an old world. but autosave is a crucial feature of Minecraft.