To clarify, there aren't that many gifs/mp4's in the game. Since I've been trying to edit videos to do my best to break immersion when characters don't match the game characters.
That said, when I test they're working on my end. So if its not a misunderstanding, then I think it must be a variable that's not switching properly.
Can you double check the settings (should be on the side panel/tab) and make sure animations are turned on then try visiting any of the following scenes?
Charmed monsters:
Alraune, giant, goblins (forest), orc, slime, squiks.
Some of those would be mountains rather than forest, but I can't remember which.
Even easier would be to refresh scenes with Pat in your room as he has 3 animated scenes.
Lastly, I did recently have someone who's browser was blocking the mp4 videos from playing. So that's also a possibility. If that happens, you can find out by temporarily switching browsers.