If you find that you're unable to access frequently used SharePoint sites, or Office 365 Groups, from Office, Office Graph may be turned off.
What is Office Graph?
The Office Graph maps the relationships among people and information, and acts as the foundation for Office experiences that are more relevant and personalized to each individual. The Office Graph uses sophisticated machine learning techniques to connect people to the relevant content, conversations and people around them.
Office Graph is a required component for accessing frequently used documents in SharePoint sites and Office 365 Groups directly from Microsoft Office apps.
How do I reenable Office Graph?
If this is just for a single user it can be re-enabled by that user by signing into the Office 365 portal in their browser (https://www.office.com), clicking the menu button at the top left corner, selecting Delve and then going to settings.
Can't find the app you're looking for? From the app launcher, select All apps to see an alphabetical list of the Office 365 apps available to you. From there, you can search for a specific app.
The settings button looks like a gear and is located towards the top right of the screen.
When you click it. choose Feature settings. Make sure that Show documents in Delve and in the Discover view in OneDrive for Business is enabled then click OK.
If you have Graph disabled for the entire organization then your Office 365 Administrator can turn it back on. For instructions on how to re-enable it see Office Delve for Office 365 admins.