Sessions aren't working properly for that website. As you may check, Chevereto sets an "auth_token" string on first session load (you can check it in the HTML source code), which must keep the same value all over that session. In your case, pikmu.com session is changing from first load to subsequent requests, meaning that Chevereto doesn't allow those requests because the auth_token isn't valid.
You will have to refer to your hosting provider and tell them that maybe there is a bad setting in cache related to PHP sessions.
Sadly this needs to be fixed at server layer, Chevereto can't fix this. By the way, in the upcoming new version this issue will be detected and the script will halt execution until this is fixed. Just warning you to ask your server support to fix this before the next release.