Okay, I figured it out. For some reason those images have a sizes="0px" property, and that makes them appear as 0px height (it's supposed to be a srcSet thing based on container width)
@gargron where else do you find one
@CobaltVelvet I mean, I need to patch this on mastodon.art asap, and I currently don't have access! Need @Curator's help 😰
@Gargron @CobaltVelvet @Curator This is what you get for not implementing backdoors in Mastodon
@Gargron aaa I was too slow
Crisis averted: mastodon.art patched, fix submitted to the repository. Embeds show up correctly now 😁
Love too find bugs in production