Well, I was about to report I too had the same problem. I'm in USA and on AT&T non-insider. For several weeks, my microphone icon did nothing, whereas previously it worked fine. Not only that, when I entered queries by keyboard, it would return a result only to close down after a few seconds and return to the tiled main screen. So just before I posted this message, I tried the microphone icon again just to be sure. Whoa, all of a sudden, the microphone is working. Only thing I did was reboot the phone, which was the first time in a long long time. The only reason I rebooted was I was trying anything to fix the default alarm app which wasn't giving me an alarm tone except for a single text received twerp. So Cortana mic now working. Alarm and timer alerts are now sounding but not using the user selected tone.