We asked Metro what was going on, and here's their answer:
Thanks for bringing this to my attention, we are looking into it. Twitter is over capacity at the moment so I can’t even get in. According to their status though, there have been a few API errors the last couple of days.@metroopensdoors is the official WMATA Twitter account and has 4,668 followers. @wmata, an unofficial feed, has 4,118 followers.