intersting. Just tried on my MacBook Pro (late 2011), iMac (late 2013) and iPhone 6S Plus and iPad Pro and you are correct, the airport utility cannot find my Airport Extreme. Internet is working without a hitch, but none of my devices 'see' the Airport Extreme. FYI, I am a dev and I am using latest betas (as of 15 AUG) on all my devices.