Most don't load for me. Just get a black screen. The ones I've checked were mp4s from imgur. Not sure if that accounts for all of them though.
Edit: I think it started after the most recent update.
Edit 2: mp4s from catbox.moe also doesn't work. It shows a spinner at the bottom but never loads.
I'm getting this issue a lot too, sometimes if you come back out to your feed and back into the post multiple times it will eventually load, other times not.
Viewed from a sh.itjust.works account. In the Card view I see a green play button on the thumbnail, but touching the image or the play button or kebab menu> open all go to a black screen with the grey "broken image" icon.
I haven't seen a video work in at least a few days; I thought it was just me. For what it's worth, almost any picture who's thumbnail card I touch is broken in the same way - just the broken pic icon.
Fyi, I just updated to the latest. I see this error and button now trying to load catbox.moe images (before, I was just seeing the image flash up for a split second and then a box icon with a zig zag through it would replace the image).