Notes on issues I ran in to:
/robots.txt can not load anything other than NOTHING or ablank document. No 404 pages, they break Twitterbot. (this will break BOTH types of validators)
Try removing the :src from twitter:image:src. It works without it, I can confirm, and it wasn’t with it, so I don’t know.
You can not have any more than 200 chars in description. I was having issues until I successfully paired this down at sentence boundaries.
Your page can not take any longer than 3 seconds to load.