For months now I have had a problem that on incoming calls people often cannot hear me though I can hear them clearly. I think, but am unsure, this happens when the person calling me is on a landline. Certainly when I test it from home using my landline I observe this effect.
If I go to connection settings/mobile networks and turn OFF VoLTE make HD calls the problem is solved.
BUT whenever the phone restarts (every day) it switches it back on so I have to remember to switch it off.
I wondered what was going on so I tried switching ON "data roaming using mobile while roaming" and ON HD/VoLTE and lo and behold it works fine - problem solved.
But why? And why cannot ~I leave HD/VoLTE switched off and rely on it remaining switched off?