OK, the can direct media has to be set on both extensions in the UCM.
I am going to take a wild couple of guesses -
When I listen to the audio, I hear one-way audio. In the audio stream, I see what might be an slight echo of some type. I hear you saying “hello”, but I do not really hear anything in response, but looking at the graph, there is something, but it always follows you and in a much lesser amplitude -
When looking at the flow, it indicates that the call is being terminated by the PBX (look for the circled BYEs) -
The reason code is 16, which is a normal clearing.
This makes me wonder what happens when the same call is made, if it is answered using the speaker phone function rather than the handset? If that works, then check to see if the handset cord is plugged into the handset port or if in the headset port.
Also, look at the UCM, PBX Settings, SIP Settings and the ToS tab, what is the RTP timeout set to?
Additionally, the UCM is on a somewhat older firmware. You might tale a look at the release notes and then consider if updating is worthwhile.