Windows 10 reporting wrong hard disk free space

I had the same problem, but a different cause. In my case when I tried to select all the files on the C:\ partition, the used space was 70 GB, but the Windows Explorer was showing 210 GB of used space.

I have looked on the internet, but no answer seemed to be helpful. I didn't have backup enabled nor old copies of windows installed.

I decided to download a disk usage analyzer called WinDirStat and I instantly had the missing space. It was a MSSQL .mdf file that was taking about 140 GB. Deleted that file and everything got back to normal.

It appears to be the System Restore that take this space. I go to Control Panel > System > System Protection > (select drive) > Configure and find out the huge size of the system restore file. It is quite weird though that the file is found in (E:) instead of (H:), despite taking the size from (H:). After clearing the system restore then I manage to get back the free space. I did remove the system restore file from (H:) as well.

Another weird thing is that the system restore is disabled for this drive (see the radiobutton selected), but despite that, it still create the system restore file.