FYI, since my Plex jail configuration was just about a few mount points, I just deleted my plugin install (which was pretty old) and re-installed the plugin from TrueNAS WebUI. The plugin offered in the WebUI had more recent release (12.3-RELEASE-p7) and version (1.28.2.6151).
Also, the reason I wanted to update in the first place was because subtitles were not showing properly (at all) on my smart TV. It works now apparently.