As for the "no response" problem: 
Please update Plex to the latest version, where the Plex team fixed 
this bug in Plex. You can also find a discussion and a detailed 
analysis of mine along with a proof-of-concept code in the "Plex 
Version 0.5.14 problems" thread in this forum.

If you see two Plex icons in Prefs > Mapping, there's two 
possibilities that I can think of:

1) You have several different versions of Plex installed. RB ships 
with two different Behaviours for old Plex versions and new Plex 
versions. Thus, if you have several different version of Plex 
installed, you'll see both Behaviours - one for the old Plex versions, 
one for the new Plex versions.

2) You have created your own Behaviour for Plex. You can remove that 
Behaviour at 
~/Library/Application Support/Remote Buddy/Behaviours/

Best regards, 
Felix Schwarz