No audio only when receiving a call from a specific number

[kuitogu]

Hello,
I am testing 3cx and it works perfectly.
I made hundreds of phone calls in/out with the ios client under my wifi at home and everything works as expected.

My only issue is quite strange:

If I call a specific number from "abc" trunk -> call works
If I receive a call from that very number (it's fixed landline) -> no audio for both of us (still receiving the call through the "abc" trunk)

Trunk is officially supported by 3cx.
Codecs for trunk and extension: only pcmu/pcma. Others have been deleted

Specs:
3cx 16.0.5.611
Running in google cloud linux debian (installed with 3cx official installer)
extension: ios 3cx client with 5090 tunnel (all calls work to other numbers/ with this trunk or other trunks under my wifi)
stun: 3cx stun
firewall checker -> passed OK


Wireshark dump made, but can't interpret anything useful so if a MOD would like to take a look I could send the dump.
I also have the call log with verbose logging.

Thanks

 

[leejor]

Are you aware of the provider, used by the "specific number"? If so, try to arrange another incoming call from a line using the same provider. Does being a "fixed landline" mean they are using the incumbent PSTN provider, or are you assuming that? Has that number called you on another device...your mobile?

See if you encounter the same issue. If so, engage your provider to trace the incoming trunk group/route to them. They may have an issue between themselves and another provider.