I added a temporary fix for this in yesterday’s TestFlight release. It seems to work for most videos, but fails with some.
This issue started due to RedGifs changing the accessibility of direct links to their videos. They provide a direct link to video files in the opengraph data on their site, this is what Arctic uses for generating link previews for most sites. Recently they made some changes, and the video link they provide will fail to load unless busting their API.
I requested access to their API several weeks ago so that I could properly fix this issue, however I have not heard back from them yet, hence the temporary and somewhat unreliable fix was added.
Hopefully I’ll be able to properly fix this issue soon, in the mean time, along with the temporary fix, I added a link attribution button in arctic, for videos hosted on other sites. So you can just tap the button to open the link in the browser if the video does not load.