I just flagged a bunch of posts of this user
https://kemono.su/patreon/user/80121432 (the first 15 or so posts on page 1), and it turned out they all were false alerts, and the videos are still alive and just need a valid referrer. So, if the admin is reading this - I'm sorry, I wasn't trying to troll/dos the flag function, don't ban please.
And in case someone else gets this "video not found" on vimeo, try spoofing the referrer for vimeo(dot)com. I used patreon(dot)com as a referrer and it worked just fine, so I think any random URL from patreon will do.