The Deleted Users folder contains DMGs of users that you've deleted. When deleting a user in System Preferences → Users & Groups, you are given the option of saving that user's home folder as a DMG in a Deleted Users folder:
Save the home folder in a disk image The disk image is saved in the Deleted Users folder (in the Users folder).
Selecting the Save the home folder in a disk image option will cause the home folder of the deleted account to be saved in a disk image
If there's nothing in the account that you want any more, you can safely delete the disk image from the Deleted Users folder, or even the entire Deleted Users folder itself.
Best Answer
Updating macOS High Sierra to version 10.13.2 (17C88) fixed the issue.