I believe that the problem has to do with the fact that you are using cloudflare. It does work on http however so that is what I am using currently.
Just changed it back to https to get the error it was throwing out in flexget.
2015-03-24 15:13 CRITICAL plugin anime-shanaproject.com Unable to download the RSS for task anime-shanaproject.com (https://www.shanaproject.com/feeds/secure/user/*******/): hostname 'www.shanaproject.com' doesn't match either of 'ssl2000.cloudflare.com', 'cloudflare.com', '*.cloudflare.com' 2015-03-24 15:13 WARNING task anime-shanaproject.com Aborting task (plugin: rss)
It basically doesn't trust the site since the certificates do not seem to be valid. If you know what is happening it is not a huge problem since you can just switch back to http but since it defaults to https it might be a problem for users who don't understand this.