With Plex 0.9.5, its developers decided that the app from now on would have the bundle identifier com.plexapp.plex instead of com.plexsquared.plex. As always, when an app changes its unique bundle identifier, it can no longer be recognized by its old, no longer in use, bundle identifier. That's why Plex could no longer be recognized by Remote Buddy.

Also, after spending some time with a packet logger, I found that some of the supported UDP commands changed slightly (f.ex. "Apple Remote" became "AppleRemote"). I adapted the Plex Behaviour to these changes as well and then ran compatibility tests for all commands supported by the Plex Behaviour. As it turned out, a few commands - like f.ex. "move to next display", "move to previous display" or "quit Plex" do no longer seem to work and/or be supported by the new Plex version. I removed these. If you have used the "Quit Plex" action, I suggest the action available under "Behaviours > Quit currently controlled application" as a replacement.

An updated version of the Plex Behaviour with support for the changes in Plex 0.9.5 - as far as I could identify them in such a short period of time - is now available via Remote Buddy's Online Updater (click "Check for updates.." in either Remote Buddy's menubar item's menu or at RB Prefs > Behaviour (lower right corner)).

Users of Remote Buddy Express - which, like any Mac App Store apps, may not contain an online updater - can manually download the updated version. Installation is as easy as downloading the file, unzipping it (if Safari didn't already do it for you) and then double-click it: 
http://static.iospirit.com/static/objectfiles/file/135/Plex.rbbehaviour.zip

Enjoy, and have a nice Sunday evening!

Best regards, 
Felix Schwarz