When you clear all cookies in the Chrome browser, every cookie will be deleted except for authentication cookies created by Google. This means that after clearing cookies, you will be logged out of every site that you are currently logged into, except for Google. Google has been quick to respond and explain why these issues are occurring. The general theory is that it is being caused by the new Chrome 69 behavior of being forcibly logged into the browser when you log into your Google account. After clicking on the Clear All button, though, Google authentication cookies are restored.
Source: https://www.bleepingcomputer.com/news/google/chrome-69-keeps-googles-cookies-after-you-clear-browser-data/