Bump for this.
I’ve tried disabling all of the plugins, switching back to Twentyfourteen, and doing both at the same time.
Still the problem remains. I tested it by adding a if (!session_id()) : session_start(); endif;function to the init hook for 2014, and printing out the session_id() in the header. Every time I go to a new page, a new session id shows. I added some error reporting code to print out the id and a message when the session starts, and it restarts regularly even when I am not changing pages.
Help please? I have really no idea what could be causing this, any sort of insight would be appreciated.