OK, I finally got CCleaner 5.42 to work, but the solution was a bit complicated:
Apparently, it is the combination of Kaspersky patch (g) and the Windows 10 April Update causing the issue with CCleaner 5.42 on my system, at least..
I restored a system image I created with Macrium Reflect Free on 4/29/18, BEFORE the Windows 10 1803 update. The image already had Kaspersky Internet Security 2018 patch (g) and CCleaner 5.41 on it. I updated Kaspersky to patch (h), then updated Windows 10 back to 1803. Finally, I updated CCleaner to version 5.42 and it no longer crashes on clean.
It would be interesting to know the order in which users installed the Windows 10 1803 update, CCleaner 5.42 and Kaspersky path (h).