On January 29, posts with images stopped going through to X/Twitter. Text-only posts were fine — it was specifically anything with media attached.
This turned out to be an issue on X/Twitter's side. Their API started returning errors when processing image uploads. We reached out to X, they confirmed it was their problem, and they fixed it within a few hours.
Everything was back to normal by around 6am UTC. If you had posts fail during this window, they should succeed on retry.