I had this problem after having created and formatted iso for installation to own. Before it worked very well, I had the 10049 I had updated from a clean install with the official at the iso 10041. I have all the walking, but Cortana became silent lol
Update build 10061 : I finally found where does this problem, the Cortona sound does not come out by the correct audio device, it comes with the first device, and not the one selected by default.