Recently, I started experiencing this issue on Chromium under Linux Mint 20.
Every time I opened the browser and tried to access a Google service, such as GMail or YouTube, I’d be prompted to login. After entering my credentials, everything would be OK until I closed the browser. Then, the story would repeat. Other websites worked fine.
Clearing the cache, trying different password stores and even deleting every Chromium file on my home directory and starting clean didn’t solve it.
What did the trick is the following:
- On Chromium, go to settings.
- Click on “Sync and Google services”.
- Uncheck “Allow Chromium sign-in”.
- Restart the browser.
This issue seems related to the recent announcements around the Google Sync API and “ 3rd party browsers ”. Note that if you try to login to Google through the browser menu it fails silently.