Plex plugin does not work correctly on FreeNAS 11 and easily reproducible in FreeBSD 11 as well.
Plex plugin installed in FreeNAS 11 jail definitely has a bug. Navigation through my libraries is not possible. This issue is easy reproducible in FreeNAS 11 as well as FreeBSD 11 jail.
Please read through the attached PDF file, which show a log dialog that I had with FreeNAS support team. Eventually they advised that that issue could be fixed only by Plex support. This will allow you fully understand the issue.