A little bit of a tough one to remotely diagnose... My father has a Spark Galaxy S7 (not the edge) and when he is out at home he misses a bunch of calls - basically they go through to voicemail and he gets a missed call text. His phone doesn't ring.

I've got him to check all the settings on the phone via Teamviewer but can't see anything on there - they're out in Wakefield, Nelson which is covered by LTE over 700MHz so I suspect his phone is camping out on 4G and not moving back to 3G when a call comes in (or his phone is not getting the notification to). We've also done the standard troubleshooting (rebooted his phone, removed / re-inserted sim etc), I am not prepared to factory reset it since I am in Wellington and they're in Nelson and can't risk anything going wrong. They're in an excellent coverage area despite being rural.

It is a bit of a drive for them to go into the Spark store and the consultant on the phone didn't appear to know too much of what is causing it however my father is blaming the Nougat update which coincidentally got released to his phone on the same week LTE over 700MHz got activated in his area. The problem also doesn't appear to happen when Dad is in town but he thinks it still may be.

Checked he is on the latest software (there is auto updates enabled on his phone) and the problem also doesn't seem to be affecting my mother who has a Huawei P10 Lite.

Any ideas?