Not sure if you've lost access to the videos yet, but you might need to pass cookies with YT-DLP in order for it to be able to grab the video. I don't have any private videos to test this on, but I would think simply passing
--cookies-from-browser chrome (replace Chrome from the list in the spoiler below in case you use a different browser) should be enough. You can also export the cookies from PH to a Netscape formatted file using an extension like Cookie Editor, and then pass --cookies [file location], in case the first option doesn't work. Worst case, that neither of the two cookie options works, Video DownloadHelper looks to be able to pick up the HLS stream correctly from the PH page on public videos, I think it functions similarly for private videos, but I honestly don't know if that's the case.
