Twitter Cards not showing in tweets


I have added meta tags for a large image summary card to a specific page, tags are showing up in source and the card validator is rendering the cards fine but when I input the url to a tweet, it is not picking up the card. Tried this directly and via Buffer, same result. Any ideas and suggestions would be warmly welcomed! Thanks


The site is working fine - I see a View Summary link in the corner of a Tweet on the web which is as expected, and the cards show up in the Twitter mobile apps.