After removing my devices from the Google Home app and setting them up (along with upgrading their firmware) in the Cync (C by GE) app, I cannot link or unlink the Cync service within the Home app. The app crashes many times when trying to enter my username and password. When I can enter my username and password, the app tells me I have no devices set up in Cync.
I'm so sorry to hear about the issues you're having when trying to link your device to the Home app. I have sent this information over to our engineering team and they ask that you provide them feedback through the Google Home app to them. They suggest including the keywords, "#Lights" along with the name brand of the lights and a short description of what you're encountering.