The primary microphone was not working anymore after the last update, and this is what worked for me (short version): I’ve manually reinstalled the update, downloading the “big” one (like I was updating from the previous Android version) and everythingis fine now.
Long version: after the last update (normally performed with the updater) the wifi and hotspot were not working anymore, so I’ve manually reinstalled just the update to fix it: it worked, but “broke” the primary microphone. I’ve just reinstalled the OS as described above to fix it, without trying the factory reset or removing/readding the hardware.
I hope it helps 
Eliana
Update: unfortunately after a while it was not working again…I tried to remove/readd the microphone module and the factory reset, but nothing… 