Why does my Lumia switch to mute when the loudspeaker is selected?

[Windows Central Question]

Lumia switches ot mute when loudspeaker is selected

Happens on a new Lumia - when I activate the loutspeaker during a call, the phone is switched to mute.
Did I accidentally change a setting? It is very consistent and reversible (unselecting loudspeaker deactivated the mute immediately)

 

[realwarder]

The time I had an odd thing like this happen I hard reset the phone and set my account up again and it worked. It's either touchscreen issue (unlikely but not impossible) or OS oddity which a hard reset will fix.

Backup before attempting. Note SMS messages are not backed up by default - you may want to enable that backup option in the Settings/Phone too.