Make sure your iPhone is up to date.
Tap Settings > General > Software Update
Latest iOS version available for a 6S Plus is 11.2.6.
Newsroom Update
Apple is introducing a new Apple Watch Pride Edition Braided Solo Loop, matching watch face, and dynamic iOS and iPadOS wallpapers as a way to champion global movements to protect and advance equality for LGBTQ+ communities. Learn more >
Apple is introducing a new Apple Watch Pride Edition Braided Solo Loop, matching watch face, and dynamic iOS and iPadOS wallpapers as a way to champion global movements to protect and advance equality for LGBTQ+ communities. Learn more >
Make sure your iPhone is up to date.
Tap Settings > General > Software Update
Latest iOS version available for a 6S Plus is 11.2.6.
It could be a hardware issue. I suggest that you make an appointment with the Apple Genius Bar.
It started with the last update.
iPhone 6sPlus