MacOS – Unable to account for 23.6 GB of disk space

I have a 13-inch MacBook Air, and have been using it for about a year now. There are 23.6 GB of memory that appear to be missing from my hard drive. About This Mac -> Storage shows 91GB of files, of which 61GB are "Other":

The command df -h agrees, showing 91GB used (command output shown below):

    Homes-MacBook-Air:~ BrandonWork$ df -h
Filesystem      Size   Used  Avail Capacity  iused   ifree %iused      Mounted on
/dev/disk1     112Gi   91Gi   21Gi    82% 23864730 5456996   81%   /
devfs          188Ki  188Ki    0Bi   100%      651       0  100%   /dev
map -hosts       0Bi    0Bi    0Bi   100%        0       0  100%   /net
map auto_home    0Bi    0Bi    0Bi   100%        0       0  100%   /home
/dev/disk0s3   620Mi  548Mi   72Mi    89%   140256   18434   88%       /Volumes/Recovery HD
/dev/disk3s2    16Mi  9.8Mi  6.2Mi    62%     2503    1581   61%       /Volumes/Disk Inventory X

However, here the problem arises, as when I examine the disk, only 67.4GB are actually used:

I have six user accounts on this laptop due to my family borrowing it repeatedly, and have run Disk Inventory X on all of them, as I was told that other users' files could account for it, as they are not visible to non-admins. None of them had more than 2GB of files. I have also used OmniDisk Sweeper, with similar results. I have seen all of the following possible problems and solutions, to no avail:

1. Swap files (they are seen by Disk Inventory X)
2. Temporary caches (restart your computer; didn't help)
3. False volumes in /volumes (checked; don't have anything weird there)
4. Viruses (multiple scans with different programs turn up nothing)

On a previous computer, I had a similar problem with eaten memory; turned out to be WinRAR generating huge .txt files, and these could be found with Disk Inventory X.