I have a single extension (ext 9150) that doesn’t receive or send audio once the call is connected. But it only happens if another extension calls ext 9150. If 9150 calls any other extension the audio works. Audio also works for incoming and outgoing external calls to/from 9150.
Ext. 9150 is on the same network as the PBX server, The issue happens when other local extensions call 9150 as well as when an extension at our remote offices call ext 9150.
You will have to check a packet capture. Set logger on in the Asterisk CLI (or sip debug on for chan_sip) and make a test call. Upload the logs to something like pastebin.