Twitter Card validated and approved. Worked twice; hasn't worked since


I’m afraid I need to add to the pile of Twitter Card not working posts…
My blog was validated and my Twitter card was approved. It worked the first time without problem. Second time required multiple attempts. Then it just stopped working and hasn’t worked again since. Confirmed and re-validated multiple times. Here are examples of where it should have worked: and

Here are their corresponding full links on my blog: and

TIA for your assistance.