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.
Looks like the Toolbox just needs an update; YouTube's constant changes often mess with downloaders. Good call testing with ClipGrab; that shows it's not on your end. Hopefully, the devs roll out a fix soon so you can get back to your workouts smoothly.