@mosseri @atomicpoet @zuck @fediversenews
This might be a problem with the local client? We're certainly sending down a valid CDN url as the attachment, and it renders just fine in other Mastodon clients (screenshot here is from my local server).
The CDN url is hosted on cdninstagram.com so I would check if you have any local blocklists in your browser that might affect that.
Alt-text is coming :)