Hello,
I too have been having problems with my personal blog. With twitter cards to validate I receive the following errors:
ERROR: Fetching the page failed because the fetcher cannot resolve the address.
Also tried http://www.s-config.com
Attempting to validate twitter card without the “www” produces the same error.
I’ve had the domain for almost 3 years but it stopped working in early September when I got a dedicated IP with my new SSL subscription. All plugins are installed properly to give out card information. Meta information appears to be in order when I view page source. And to verify DNS has replicated with new IP I checked my site using Tor proxy off of a server from another country. All passed.
I set my robots.txt to allow twitterbot full access to my site.
If there is something I am missing please let me know. Thank you for your time!
edit 10/13/2016: For reasons unknown my twitter metadata is now working correctly. So to whoever resolved the DNS issues on twitterbot. Thank you very much!