This can occur when OneDrive for Business has the wrong cached credentials. The fix is usually to log in to your site using Internet Explorer, which will share it’s credentials with OneDrive for Business.
In your Windows Control Panel, open the “Credential Manager” – Under “Windows Credentials” find the section for “Generic Credentials” and remove any credentials that start with something like “MicrosoftOffice15_Data” or “MicrosoftOffice16_Data.”
Then, log in to your site via Internet Explorer, and make sure you click the “Keep me signed in” box on the login page. Then, try pressing the Sync button in the library again.
