Thanks for the reports. If you haven't come to the conclusion already, this is a Google Voice infrastructure bug. They have an open ticket on it, and they accept that it's serious. The engineer I spoke with invites y'll to post specific examples, as many have done already. It's not universal, for some unknown-at-this-time reason.
There are a lot of "balls in the air" at this time, in GV-land, with some infrastructure changes related to the GV VoIP beta, etc. It's making things difficult to isolate, and they have a pretty small staff to distribute work on bugs.
If/when I have any further details, I'll be happy to share, but that's all I know this afternoon.
Again, please post over on the thread here:
https://productforums.google.com/d/topic/voice/Unn7jCk1JUA/discussion