All right, I guess the automatic insertion is still a bit ropy so using 'Insert other media' to insert them like the old image button might be more reliable.
In your case though @jackophant there is clearly an issue there, from looking in the console that particular URL is causing a parsing error so my guess is that the inserter is struggling to read it as the URL of an image. It is quite unusual for an image to not have any kind of extension, so it's probably just a bug. For now I can only suggest attaching it or throwing it on imgur.