Google has confirmed that this issue has been fully resolved.
Posted Jun 07, 2017 - 15:09 PDT
This issue seems to be resolved now. We will continue to monitor before marking resolved and will keep status at "Degraded Performance" until the all clear is given. The root cause of the issues (high latency in our Google AppEngine requests, acknowledged by Google) seem to be gone and calls are now completing normally. We will be working with Google to provide a more detailed post-mortem shortly.
Posted Jun 07, 2017 - 14:35 PDT
The root cause of this issue has been identified and is being actively worked on to mitigate. Updates to follow.