In this case, you’ll need end-to-end (E2E) traces.
To pinpoint the issue, E2E traces are essential to determine why the RTP packets are missing.
This seems like a Core issue.
Check your PCAP to see if RTP and RTCP packets are being received consistently.
I believe there’s a configuration that drops the call if RTP or RTCP packets are missed for a certain duration.
Core team said it might be a UE-related issue.
Lol, that usually means they’re too lazy to investigate.
Ask them if they have any proof to support their claim?
Friends I am also a core guy. 
Great. 
What do you think?
Might be UE issue?
Two-way audio is confirmed, so we can’t conclude that there’s no downlink RTP.
I also believe it’s a client-side issue.
And it’s only observed on one specific device.
Haha. It was only light hearted joke.
I was core test manager 
This device is the first 5G phone in the US.
If it’s not happening on any other device, then that could be the case.
However, I thought you mentioned it was happening on more than one device. Is it occurring on one specific type of device or just one handset?
Just one handset.
We will try with a different handset today, and I’ll update you.
I believe it’s due to RTCP (not RTP), since there hasn’t been any mute period during the call.
Please also check the option to disable RTCP at the network level.
It’s not applicable for now.
The issue was resolved after changing the handset.