windows - Extreme difference comparing directory size vs. used diskspace

On a Windows Server 2019 Enterprise, we have a disk with just one directory.

When we check the properties of the directory, the summary of file sizes is more than twice the amount of diskspace used (see picture)
When we do a "dir /s" on this directory, the numbers are about the same.

What's wrong with the directory properties dialog?
No symbolic links or directory shortcuts...