I can tell from a few other posts, but there is no definitive explanation. There is some kind of problem with the latest version of CCleaner, (v5.69.7865 64 Bit) which downloaded and installed two days ago. My personal experience is that I like to leave CCleaner open in the background, so that I remember to run after I close all open programs/windows, (otherwise, I sometimes forget). So then, when getting ready to run CCleaner after leaving it open while working, (and after closing open programs) the CCleaner interface is frozen. However, the "x" to close works, so I close and then restart CCleaner to clear the hang, whereupon CCleaner works as it normally does. I run the registry tool and custom clean and healthcheck at least once a day.