Now that I have upgraded to iOS 10, sometimes when I open an app, my screen will go black. I can sometimes bring it back with the home button or with the shutter switch on the side.
iPhone 6, iOS 10
I updated to iOS 11.0.2 and I am getting the same behaviors. It’s bound to be a bug in some part of the system.
First (and easiest) is a restart and/or forced restart:
Restart your iPhone, iPad, or iPod touch - Apple Support
Next (and more drastic) would be a restore from backup and then restore as new:
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
This article may also help (although I don't think it is really your issue):
If your iPhone, iPad, or iPod touch won't turn on - Apple Support
iPhone 6 screen goes black after iOS 10
