CurlException: 6: name lookup timed out

Error message such as these

fb_api_check_session failed.: name lookup timed out 6
CurlException: 6: name lookup timed out

indicate that facebook's SDK is failing. And you can't expect anything to work properly until this is resolved.

While this is probably a problem with your server's DNS setup (i.e. /etc/resolv.conf), you may have luck with the workaround described in the issue queue.