I've had the Nest cameras for a few years with no issues. For over the past month I have been unable to log onto the cameras. I am receiving messages stating an unknown error has occurred try again later. I have made several calls to customer service and have been on the line for hours with no logon success. Customer service have walked me thru deleting and reinstalling the app, try logging on with a different device, changing my password, adding google home app, and several other customer service tricks. All to no avail. I am unable to sign in under Nest and also Google.
Thanks for reaching out here in the community. I know that you've been through a lot of troubleshooting and I wanted to dig deeper into this. To confirm, have you migrated your account to Google? When you open the Nest app, do you select the "Sign in with Nest or Sign in with Google"? Have you tried signing in to a web browser and going to https://goo.gle/2qjvVSU or https://goo.gle/2UZL8VI?
Looking forward to your response.