Posting to Social Media changes everyday - and today is no different. Twitter is going to refrain from cropping your images to a 2:1 landscape view. This change is also retroactive, so you don't have to go and change your old posts. You can view your history and see them without being cropped to a landscape format.
Not to be forgotten the gallery card has been updated so it no longer displays 4 equally sized images but, a new larger main photo along side 3 smaller images.
So far this affects only Twitter.com, but we should expect to see this probably roll out on their mobile apps soon.