I can definitely see that something about local vars is broken. But please ignore that earlier min working example for time being. It breaks on emacs-25 build too.
All I know for sure is that the comment-start being undefined error never showed up on emacs-25 builds, and it showed up for the first time on the latest master build as of today.
So I will try to derive a min working example by studying the outshine.el code. But in the mean time, if you can quickly review why comment-start could be in undefined state momentarily, that would be great!
I'll keep you posted.