CCleaner Drive Wiper jitters, stops, but seems to work?

Hello there,

I was recently running CCleaner's Drive Wiper on a computer I planned to give away. I let it run and let it do its thing. However, midway through the process, CCleaner respawned the window (so, it kinda jittered, like it was trying to continually relaunch) and closed, not giving any indicator of progress. I reopened CCleaner from the desktop and nothing indicated what happened. Before I restarted, I noticed a folder full of "Zzz.zzz.Zzzz" files in C:\\ . I restarted the computer and the files were gone and everything seemed intact. What could have happened here? Should the computer be okay?