Q: Iphone hanging up on me after upgrading IOS version

Hi,

I have an Iphone 6 128gb model. When I bought it it had IOS 8 pre installed on it. Everything was running smooth until I upgrading my IOS8 to IOS9. It started hanging up on me at random intervals. From screen blacking out on receiving the calls to phone not responding after touching the screen. It is like phone getting clogged with pending commands and then suddenly it would respond complete the action.

To fix the issue on my own, I formatted the phone to factory settings and restored my back up on it but it did not help as the phone was still acting the same. I then again formatted the phone to factory settings but this time did not restore my data and used the phone for next 24 hours without any previous data. The phone worked smoothly and the problem was gone. It proved the problem is with my data.

Now my question is the same data was working smoothly on IOS8 but not on IOS9. Why?. The data is important to me. Is there any way to find out which file is giving a problem so that I can delete only that one? Or is there a fix for it without deleting the data like going back to IOS8 or any other fix?

Please help!