30 seconds of what? Is it 30 seconds of ringing then it gives up, or 30 seconds after answering? I can't tell from that Wireshark screen shot.
Here's a tip when you've got a capture that might have more than one SIP dialogue in it - drill down in to the SIP packet until you see the header "Call-ID", right click on that and "Apply as filter > Selected". That will filter to just that one call.
From those session timers you've set, it looks like you're trying to disable them. If that's what you want, set them to 0.
Yes, you can re-use COS/COR as many times as you want, assuming the settings are appropriate. Given that you are using the same COS for two peers but only one has the issue then I would say that it is not a COS issue. There are call duration timers in COS but these are a minimum of 2 minutes so it's not that [and it doesn't force a clear down, either].