This may be related to an app conflict. There are three things I've tried that seem to help.
1) Double-tap the home button to see the apps running in the background and swipe up on each one until they're all gone (except the home screen).
2) Delete any apps that you don't need or use.
3) You should also go to Settings, look through your list of apps, and tap each one to see what kinds of things they're doing in the background. You can set Location to Never or While Using the App instead of Always, turn off some or all notifications, and turn off Background App Refresh. Check all your apps and only allow the things you need turned on.