Symlink for iTunes device backup location stopped working

I've been using the tip documented here (Make a split library portable - Apple Community) to "re-direct" iTunes for Windows device backups to a different drive. Recently, this has stopped working in a strange way. New backups get created in the new location, but iTunes no longer "sees" the backups. The list of device backups in Preferences->Devices is blank and the "Restore Backup" button when viewing an attached device is greyed out. This seemed to have happened with the latest update to iTunes from the Windows Store (V 12.13.9.1).

Is anyone else using this symlink/junction method seeing this issue? I've contacted Apple Support and their response is that since this is not an officially supported method, they could not help.