This is because you have signed multiple Microsoft accounts in your browser, then it caused such a behavior. To resolve this issue, you can open an incognito window in your browser and access the resources you need with your account. Another way is to remove all Microsoft related credential in your browser. To do this, go to settings > passwords in your web browser, then search with "microsoft", and you can remove all the saved accounts now. 

https://answers.microsoft.com/en-us/msoffice/forum/all/error-message-you-signed-out-of-your-account-its-a/7cd0834f-46fe-472d-ac71-