Your trouble is likely:
If downgrading (or upgrading) doesn’t help:
It’s hard to read the log because you have all the DEBUG stuff but none of the higher level (VERBOSE, NOTICE, etc.) for context. Also, the SIP traffic would be useful.
Do you have the UDP port range for RTP (default 10000-20000) forwarded to the PBX? What kind of router/firewall do you have?
Have you tried using pjsip for the extension?
You seem to be using g722 on the extension side. If there is no benefit (because the trunk is alaw), try allowing only alaw and see whether it makes a difference.
The extension seems to be on a cable modem / Wi-Fi – is that correct? If so, does it fail the same way when using mobile data?