How did you disable Little Snitch?
I just tested, and get the exact same symptoms with Little Snitch. PMS seems to work, but crashes instantly if the DLNA server is started. Disabling the DLNA server seems to prevent the crash.
Disabling Little Snitch from the menu isn’t enough. You have to delete /Applications/Little Snitch.app to uninstall the problematic Network Filter.
I never saw these crashes until I started testing with DLNA enabled. So the other choice seems to be disabling the DLNA server in Plex.
In Terminal:
defaults write com.plexapp.plexmediaserver DlnaEnabled 0
