I have this same problem, when I use latest CCleaner update, on my iMac running High Sierra, with latest OS updates.
I've found a quick, much less frustrating work-around, instead of typing-in my iMac password, so many times, to allow the CCleaner to clean the caches on my iMac:
Start CCleaner.
Run the cleaner.
At each password window, disregard filling-in password, leave blank, and click cancel button. Repeat this twice, or each time the Mac wants your admin, password.
So that translates into: Click Cancel button twice, at blank password box, and CCleaner cleans the caches, (quite quickly on my iMac).
Easy way to see CCleaner is working:
Wait until after first run through, not filling in password and hitting Cancel button, leaves you at results window. Double click on any folder listed and then copy the route Cleaner used to clean that cache. Then go to Finder, click or type in your main HD, and follow-out that routing, to the cache itself, and you'll see, it was cleaned out.
I recheck this routing out, once per week or more, and Cleaner is still working in this latest version! (Though I will admit having to click the cancel button, twice or more, just to get CCleaner to do its cleaning rightly, instead of just hitting the main Cleaner button once, and it working the way it should, IS a real hassle. However, I will admit, until CCleaner experts, find the problem and correct it, then give us customers a patch update that fixes this problem, that clicking the cancel button twice, so fast, doesn't take up much time!)
This is the only way I've found, to make this latest version of CCleaner, actually clean the caches on my iMac. Hope this helps-out other Mac users somehow, running CCleaner App.
Snaggletooth
