Update #1: iOS 9.0.2 is released.
Update #2: Issue confirmed in isolated cases at Apple forums
View the latest data here.
We are getting a lot of data now which takes time to put together. I've forwarded the document, which is being updated daily, to Apple's engineering team.
Many users have found out that their iPhone 6S, 6S+ (some 6) turns off by itself, even when left unattended. It is fixed by forcing a restart of holding the home and power button for 10 seconds. Had this issue? Read below.
iOS public release users:
Please post your model, OS, and actions before the problem occurred.
iOS beta users:
Please post the same info as above, but also report it through Apple's bug report.
iPhone 6S 64 GB Gold
1. Plugged iPhone 6S to USB on Windows PC
2. Changed region to US where iOS restarted itself automatically
3. I didn't see the Apple News app so I restarted manually with the power button
4. I checked a few minutes later and the home button nor power button could wake the device
5. I restarted the device holding the home and power button for 10 seconds