I have a few questions myself, too, though ;-)

1) Any reason why you’d use a Plex setting to sleep your screen (for which there is no public API) when this is also available via System Preferences?

2) Do you use the actions in Remote Buddy’s Plex Behaviour - or do you forward button events from Remote Buddy to Plex using Remote Buddy's Virtual Remote? Or, in other words, what does your mapping table at Prefs > Mapping > Plex look like?

3) Have you installed and do you use the Apple Remote driver supplied by Remote Buddy (Candelair)?

4) Please run Remote Control Diagnostics (free download from the Labs section of this website) when the problem occurs and copy and paste the full version of the output here.

This information should help a great deal to get a better idea on what is going wrong on your system - and hopefully provide a solution.

Thanks in advance.

Best regards, 
Felix Schwarz