Though OneDrive is a great tool - there can occasionally be issues which cause synchronization (between one of your devices and OneDrive) to fail.  This could impact a small number of files or folders, or it could stop the sync complete. 

Below are the various OneDrive status icons which indicate there may be an issue.  These will show in the taskbar or notification area (bottom right in Windows, top right in MacOS).  If you can't see any OneDrive icons in the taskbar or notification area, it could be that the icons have moved, or OneDrive isn't running. Learn more.

OneDrive Status Icons

Below are some of the more common OneDrive status icons, what they mean, and a link to details on how to resolve the issue.  For more information, see Microsoft's OneDrive Status Icon page.

Windows 

  OneDrive work/school sync error

macOS

  OneDrive for Mac sync errors

Windows File Explorer / macOS Finder

  OneDrive sync error

  OneDrive processing changes

  File locked 

Common 

  or    OneDrive processing changes

  or    OneDrive paused

  OneDrive not signed in

OneDrive reset

If other issues have not worked, you can reset OneDrive.  This will not delete or alter, any data on your computer, or on OneDrive but resets the synchronization.  It's a catch-all troubleshooting step for most issues.

Last Resort / All Else Fails - Reset OneDrive Client