Hi Nick,

As I suggested to Kathryn who is having the same issue - it's a Twitter change/problem. It's happening on their own page that talks about embedded timelines. If you scroll down you'll see they're not displaying their own tweets.

https://developer.twitter.com/en/docs/twitter-for-websites/timelines/overview

Twitter might fix this issue. Otherwise you may need to remove it. If you've got a Twitter account I'd recommend tweeting them!

Sorrel