This iPhone 7 (Model 1660, 1778, 1779, 1780) is running iOS 11.2 (15C5110b), which may not be supported by this version of Xcode.

Same here -- production (not beta) release of 11.2 on 2 devices. Release version of Xcode 9.1 can't run against it. I don't see any updates in the Mac App Store or in the Developer website.

This has happened before -- why does it recur?

But more important -- where is the appropriate version of Xcode?

I understand this has been a hectic week with the root problem and new hardware still coming online, but still..

Does anyone know where there might be an updated version of Xcode? Or should we be using the beta version of Xcode? (To make a minor patch to a production app in the App Store...)?

There's no update just yet. While that happens you can use the latest Xcode Beta release (version 9.2 Beta 2).

https://developer.apple.com/download/

Same here on my iPhone X. (no device support files, no Xcode update available)

To put it nicely, Apple's had a cascade of unexpected problems with their recent iOS and macOS updates, no doubt overwhelming the release teams. I'm guessing 11.2 was rushed out to address the Dec 2nd date bug (some users' phones would crash over and over with certain local notifications).

It's incredibly inconvenient, but I think we'll just have to wait this out. If anyone has a nice hack/workaround I'm all ears since I was counting on doing a lot of device-only stuff today.

wait unitl Apple release newer version of Xcode...

I'm getting the same message. From the look of things Xcode 9.1 doesn't have support for iOS 11.2. It's not even an option as a deployment target.

Xcode 9.1, as you discovered, won't recognize a device on iOS 11.2 -

Note 12.4 - Xcode 9.2 release should be in the MAS today.