I got same issue, after add the codes in http://docs.wordfence.com/en/I_enabled_Falcon_Caching_and_my_site_errors_out._What_went_wrong%3F
issue would be solved for temporary, and it would be 500 error again.
So, I check the .htaccess, I found wordfence add some codes before all other codes, I deleted it and change the file access from 604 to 404 for prevent wordfence add codes in it again.
And Falcon Engine works fine now, so maybe there's some bug need to fix.