Player card privileges seem to have been revoked


We had been using the player card, quite happily, for months. Approximately 3 weeks ago, it just stopped working for us. Logging in, it seems our card had been revoked. I reapplied and received the following in an email:

The URL you provided for to use the player card did not validate. Please make sure the page contains valid metadata, then reapply for a Twitter card.

Checking the following page though: all of the metadata seems to be present as expected. Is there are reason why 1) our card was originally revoked after having been working for so long and 2) our metadata is showing up as invalid, when in actual fact it seems to validate perfectly fine with the dev validation tool?