Thanks for fucking up a fine product.
Cannot download shit from Youtube thanks guy's.
There is also a fork at https://github.com/OpenHelios/clipgrab-qt5
Chances are you're using a version older than 3.6.8. YouTube in particular, and probably other sites as well, don't condone downloading and change things around to prevent programs like ClipGrab from functioning properly. As of today, 27 Feb 2018, version 3.6.8 works perfectly. (Also, the program is free. The authors were kind enough to share their solution to a problem with you and don't deserve abuse. They OWE you nothing.)
I know I should be constructive but I am pissed!!!