Despite having Secure Deletion option set to Normal (Faster) it's taking 15-18 minutes to delete the thumbnail cache (about 3Gb in 1,700 files) of an old version Paintshop Pro using Custom File and Folders in Custom Clean, compared to 1-2 minutes in Explorer.
The files aren't being "wiped" as I can still restore them with Recuva, they appear to just be normally deleted, veeerrrrryyyy ssslllloooowwwyyy...
I did notice some increase in activity from Windows Defender during the deletion, which could be a clue, or a red herring