Deleting orphaned WIM mounts gives error 0x80070780: The file cannot be accessed by the system

Long time ago I mounted a WIM image on S:\mount without un-mounting it. The image file has since been damaged and deleted, but the mount point left intact. The drive letter has also been changed for whatever reasons (so it's D:\mount now).

When I try to delete D:\mount from Explorer or Command Prompt (elevated), I get this error for the thing:

Error 0x80070780: The file cannot be accessed by the system

I have run several chkdsk.exe /f D: and rebooted, but that directory hasn't been deemed "bad". I also tried deleting the folder with IObit Unlocker, from within Ubuntu (with ntfs-3g) and from another Windows installation (Windows To Go and Windows PE), but none proved effective.

I need to delete the folder (orphaned WIM mount point) without formatting the volume.