System: Windows 10 with latest upgrades. CCleaner 5.28.6005 (64-bit)
Pointed the Duplicate Finder at two folders that were thought to be nearly identical. Each contained a dozen or so files and half dozen subfolders, each sparsely populated. Ran the search, and it found about ten dupes in the top level. Selected one of each dupe, then hit Delete Marked Files (or whatever). Progress bar stopped about halfway through. Explorer seemed to hang; was unable to bring up Task Manager or a new file explorer to check the progress of the deletions. Had to crowbar the system. On reboot, found that some of the selected files had been deleted, but not all of them.