Allow synchronisation of files that include special characters in the filenames, like # and %.
Step 1; Download and install the ‘SharePoint Online Management Shell’
Step 2; Open the SharePoint Online Management Shell by searching for ‘sharepoint’ in your startmenu.
Step 3; Run the following command: (replace the values according to the tenant you are connecting to)
$userCredential = Get-Credential -UserName $adminUPN -Message "Type the password."
Connect-SPOService -Url https://$orgName-admin.sharepoint.com -Credential $userCredential
Enter the password, click OK and press ENTER.
Step 4; Run the following command:
Set-SPOTenant -SpecialCharactersStateInFileFolderNames Allowed
All done, it can take hours or even a couple of days to get the files to sync after the change.