This must an easy task for warming-up after your holidays:
the twitter card meta's are not closed ( />).
Thanks for the great job you're doing.
For those being in a hurry, just edit the .../wp-content/plugins/wordpress-seo/frontend/class-twitter.php
and at the end of the lines that contain: <meta name="twitter: etc
replace the '">'
with '" />'
at echo "<meta name='twitter:image' is there an error at the end of the line (#122)?