One way audio

[jthjthjthjth]

Anyone having trouble with voice calls suddenly going to one way only?

Each evening I tend to have a Vodafone to Vodafone call with a family member. Of late, if  person A is speaking for a long time person B is then unable to reply, as though their microphone has been muted. We have to drop and re-establish the call to carry on. 
Person A is driving in Southampton using hands free kit. Person B is in Leicester. This has started happening since A has swapped from an iPhone 8 to the latest iPhone SE, which means A now has 5G capability. B has on early iPhone SE which can’t do 5G, although the timing of the phone change and the start of the problem might be coincidence. I’m wondering if this might be something to do with 3G switch off and the call being now carried by VoLTE. 

[Mark]

If both phones aren't setup to use our 5G network @jthjthjthjth, then the call will be moved to a network that both are compatible with. You mentioned this has only started since person A started using a new phone via a hands free setup. Does this happen on calls all calls made by person A on the new phone, or just calls to person B. Are you also able to see if the loss of audio happens if the hands free kit is removed from the equation?

[jthjthjthjth]

Removing the hands free kit is tricky, given motoring legislation. Our next experiment is to disable 5G on A’s handset. Things have been fine with the iPhone 8 and the vehicle’s inbuilt hands free setup. So I’m guessing that either the new iPhone isn’t playing nicely with the hands free, or that 5G is a factor. With the iPhone 8 the voice call seems to be established via circuit switched 2or 3G since find my friend stops working for the length of the call, ie the data link drops. With the newer phone the data link stats up so I’m guessing VoLTE is being used. 

[Mark]

I wouldn't suggest you drive and use your handset at the same time @jthjthjthjth, but maybe make a call when person A isn't driving and connected to the hands free kit.