Apple TV 4th generation model A1625, tvOS 11.0
Minecraft Apple TV Edition Version 1.1.5 (last updated 8/7/2017)
same issue. Have deleted all iCloud data for the app and deleted the app, rebooted Apple TV and reinstalled the app, XBOX Live signin is still broken and just flashes a message about connecting to XBL. Never able to actually sign in.
edit: Issue seems specific to Apple TV Edition, I am able to sign into Pocket Edition on my iPhone running iOS 11.0.1 with no issues.
+1 bought this forsaken version, bought it also for desktop, iOS, and android. My kids get so frustrated that this doesn't work right on the apple tv, it's really pathetic that one of the most expensive versions is the least supported.