Apologies if this has already been posted. There is a growing issue in the last few days/weeks with AirPort Extremes and TCs where they are disappearing in the AirPort Utility and also disappearing as an available network disk (in the TCs case) as well as for a Time Machine disk. They feed internet and IPs etc. Most importantly for me, my Time Machine disk in the TC vanished on the network. It was still there with all backups after the fix but at first I was worried the TC had bricked or had s@#t its self. Basically the green light is on but the TC/Extreme disappears from the AirPort Utility and Finder and Time Machine. Seems to be happening to a lot of people (including me) and is well documented on this site: https://www.macintouch.com/forums/showthread.php?tid=471 FIX: Remove Back to My Mac Apple ID/s. This may be difficult to even get to the app to remove them. The way I found was to hard rest the TC, then import a backup and them immediately remove the ID/s before you reboot. Alternatively, if you do not have a complicated setup you can hard reset and then rebuild the setting but avoid adding in the Apple ID/s into to Back to My Mac section. Apple PLEASE FIX THIS. Note, it happens with both ElCapitan and Sierra for me so it is a TC/Extreme issue, not OS.