My iPhone 6s is glitching like mad after the iOS 11 update, what should I do?
The first thing I’d try is downloading and installing the iOS 11.01 update.

To install the update over-the-air, go to Settings > General > Software Update.

For more information, refer to: iOS 11.0.1: What’s New Or Changed?

Finally, if you get absolutely desperate you may want to consider Downgrading iOS 11.0.1 To iOS 10.3.3 / iOS 10, though the window for doing this will be short!

Long term, like any iOS problem where multiple apps are misbehaving, you can always erase all content and settings after you have a good backup to make sure it’s not your settings. If the glitches continue, then restoring the device will get you a clean speedy iOS or the knowledge you need a hardware repair.