I’m having the exact same problem.  I randomly lost microphone functionality in the middle of streaming in discord.  I’ve done all of the above steps multiple times to no avail.  I can confirm the mic is working via Synapse Mic Monitoring “sidetone”, but in Synapse “Mic Preview” can’t detect any sound.  Neither can windows or any apps.  I’m at a loss.  

I walked across the house with the headset on.  It gave the beeps warning I was out of range, but I could still hear the audio the entire time.  When I returned to my desk, this issue happened.  I also did use the Razer pairing utility to plug in and re-pair in case this was some kind of out-of-sync type issue.  This did not work either.