I used "Wipe Free Space drives" and checked "Wipe MFT Free Space". I choose "Secure file deletion" and checked "Wipe Alternate Data Streams" and "Wipe Cluster Tips".
Immediately after CCleaner finished I used Recuva and 21 files were found and recoverable.
It appears that you are running deep scan in Advanced Mode, and that the 21 files were all found during the deep scan. Can you let us know what is checked in Options/Actions, and is everything checked in Options/Drives?
I'm surprised that nothing from the MFT is shown. Wipe MFT replaces real file names and info with dummy file names, but they should still be shown in Recuva.
I am perplexed by this. As I posted above, why aren't the deleted files in the MFT being shown? Whenever I've run a wfs for testing (on a small device) the files that CCleaner uses to overwrite free space are visible using Recuva. Where are they?
I don't know why 21 files are being listed by Recuva. They add up to around 1 mb, so it doesn't look like an odd cluster or two.
Unless there's some very clever way that CC works, the file names in the MFT are overwritten with dummy file names. So they're still there as valid file names, but of no use to anyone.
Unfortunately, unless I have a brainwave, I've run out of ideas on this one. I'll try to rig up a spare drive to do some tests myself.