This is the second time it's happening. After expanding my world to above 500MB, it starts not to sync properly and the saved world picture is a generic black and white picture. Eventually, it will come to the point when the file size becomes 0.1MB and when trying to load it, it will say the file is corrupted. Thinking it could be a hardware issue, I sent the console for repair at Microsoft. It was returned and I was told it was all ok and the console was reset to factory settings. After losing one world, I set up a new one. Again, after the size of the world goes above 500MB, the problems are starting again. I've tried a hard reset. I've changed from wifi to wire internet and nothing helps.

Is it a hardware or a software issue? Could the hard drive be faulty?

I have written to Microsoft Support but there was no help provided. I have written to Mojang and they say its a local issue, which I presume is the console. So I'm being passed from one person to another without resolution.