I can't let such a complete problem report pass without expressing my appreciation for
it. Perhaps you've actually read this:
https://groups.google.com/g/video-downloadhelper-q-and-a/c/BzPLK2YyL-s
So many people seem to have missed it.
I had to try the page whose URL you gave. I saw one short video at various resolutions,
one of which I successfully downloaded, & it played fine. But that was on Firefox so I'm
not really doing anything but confirming your observation. I don't have Chrome so I
can't comment on that. Somebody else is going to have to step in to help you with that.