Cloud accounts · Custom Google sign-in credentials
Why does my Google account stop working every seven days?
Short answer: Your custom credentials' Google project is in testing mode, and Google expires those sign-ins after seven days. Publish the app on your project's consent screen, then add the account once more and it stays signed in.
Because the Google project behind your custom sign-in credentials is in testing mode. Google expires sign-ins made through testing-mode projects after seven days, so the account stops working until you add it again.
To stop it, open the consent screen of your Google Cloud project and click Publish App. You're not really publishing anything — nobody else can use your credentials — it just tells Google this isn't a temporary test. The in-app guide's last, optional step covers this. After publishing, remove the account in Storage Studio and add it once more.