Apple has released an update to the AirPort Extreme and AirPort Time Capsule firmware.
Firmware update 7.7.2 is for AirPort Extreme and AirPort Time Capsule base stations with 802.11ac.
This update: ● Addresses an issue that prevents a USB hard drive connected to an AirPort Extreme from appearing as an available disk in Time Machine ● Resolves an issue that may intermittently cause a loss in WAN connectivity ● Resolves an issue that may result in a network loop