Downloading Videos from Youtube stop working

Hello, there!
This has happened three times so far now, so I am submitting a request. I download several videos at a time to trim and then use in exercising. After about 2 downloads, no other videos can be downloaded.
I tested by downloading from a website (one succeeded but others failed) and clipgrab, which worked on the failed videos. Now I know that the Toolbox needs an update or something. Google is constantly changing youtube to prevent downloading, but I am not sharing or otherwise violating any terms. I just want to exercise without stopping or skipping ads.