There are special characters you cannot use in filenames because they serve other purposes within OneDrive and SharePoint. If you have a file that has a special character, OneDrive and SharePoint will not be able to sync. The best thing to do is rename/avoid using these special characters. Don’t use the following characters in filenames on OneDrive or SharePoint: " * : < > ? / \ | If you have a file or folder with any of these invalid characters, just rename and syncing should continue.