hard drive - Harddisk space used by unknown data on Windows 10

I'm really stuck on a problem with two of my drives (1 hdd + 1 ssd):
Both show they are almost full after I have cleaned (wiped) the free space of the drives using PartitionGuru. (that finished without any error)

According to recommendations from the forum I have checked the drives with WinDirStat and Treesize (both running with SYSTEM priviliges) with the following results:

The drive is a 120GB SSD (showing 111.8 GB in windows) with shadow copies etc. disabled
WinDirStat showing 78.5 GB of data, 31.7 GB of and 1.7 GB of free space
Tresize showing 78.5 GB of data and 1.7 GB of free space

My second drive (a 1 TB HDD) even shows several hundred GB as unknown.

I have tried all I could think of - but i couldn't access the "unknown" data. How can I get the free space back?

Thanks

Edit:

Disk Management:

Answer

After running Chkdsk over the night for the d: drive. That one seems to be fixed.
So I guess that is the solution.

I ran the following command: chkdsk d: /r /f (for the d: drive)

(I ran it with SYSTEM priviliges)