Hi,
I noticed that Android 5.1.1 has a battery optimizer that automatically turns off an app after 3 days of not opening it.
That affects the "Norton family app". Once optimized, the app is useless, allowing you to browse any webpage.
You'll find it in settings/system/battery/app optimisation/detail.
Could you have this in mind for your next update? Otherwise it just doesn't work.
MT