I really don't think it's software related. Microsoft had to replace one of my phones. I am in the process of finding out why one was repaired and the other was replaced. The one repaired had a cracked screen as well as a broken speaker phone function. So
I paid for the repair, it was very quick only 4 days.
The second phone had only the broken speaker phone problem, so it was done under warranty. It also was done very quickly. Only, UPS the courier, lost the phone and the investigation took over 3 weeks until a second replacement was sent.
Perhaps the broken screen was replaced and with it other parts of the phone so the microphone was also repaired accidentally. I have emailed the repair company used by Microsoft, they are called Anovo, asking why they were unable to repair it and sent a
replacement phone. Currently waiting for a response.
Also I noticed an updated firmware has been released. Firmware not an operating system (software). I thought maybe the firmware is what fixed the problem. So I went ahead and updated the firmware before I sent the second phone. This did not work. The firmware
is not updated automatically, you need a special Nokia software to do this.