I’m a developer (please ignore/forgive the NFT stuff).
It may be a problem with your browser or lemmy-ui, you could try with a different browser and/or open an issue on the lemmy-ui github repo.
Some instances are under a fairly heavy load at the moment, gifs are fairly big files, so it could be that.
If you try to download the gif directly (copy/paste the url into the browser’s url bar) it will probably return 502 Bad Gateway
if that’s the case.