Just to be clear, this specific symptom (calls from one GV/XMPP endpoint to another ring, but the session doesn't set up, thus not sending/receiving audio)
was/is not caused by GVGW. Some GVGW users have posted issues that may have had other root causes with their GVGW/SIP/OBi configuration, which could complicate identifying the actual issue.
Is anyone still having this issue? I chatted with one of my contacts at Google Voice today. In this scenario (one GV number calling another via XMPP), the calls are "on-net", meaning that they aren't traversing the PSTN, but instead, carried over the internal network. There have been some isolated incidents of the called endpoint ringing, but the call setup doesn't complete, so there's no audio stream. It hasn't been widespread enough to identify the root cause, so if this goes down hard again, they can investigate it further.
As a side note, as with most large companies, software and infrastructure changes are coming to a year-end freeze, and this means, on the plus side, I don't expect anything else to mysteriously break.
On the minus side, if this issue surfaces again this month, I don't expect anyone will be able to work on it.