I want to share that I’ve had the same experience of Twitter player cards initially displaying “media forward” without requiring viewers to click on “View Media.” It’s part of the reason we implemented player cards on our site. Now, all that folks see is the url with the “View Media” link. Very disappointing and definitely a change in behavior.
As evidence, a ticket that I opened in May 2015 dealing with the placeholder image not displaying correctly: Player card black background placeholder image. “Came in this morning, opened up the timeline, and an image that was working successfully yesterday had broken to display a black placeholder image.”