Update 3 - August 21 2017:
Seems like the SIS sync system was updated to help increase performance with the syncs. Our instance has NOT been updating since August 15th, so hopefully things will be up and running again soon.
Sounds like "grade-passback" is becoming "grade-passback connector for PowerTeacher Pro" which may have additional features that I am only able to find bits-and-pieces of information about.
Based on the most recent communication regarding the PowerTeacher Pro Grade-Passback Connector, it seems that there are a few known bugs that are being worked on. It seems the expected timeline for full implementation should be by the start of next week (August 28th 2017).