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Thanks for asking.
I'll more information from you before I can answer your question:
1) Which version of Remote Buddy and Plex are you using respectively?
2) Do you have Remote Buddy's driver (Candelair) installed?
3) Please provide a screenshot of Preferences > Mapping > Plex
4) Please provide a screenshot of Plex' remote settings
5) Is "Plex Helper" running (please check in Activity Monitor) at the time you experience the issue?
Thanks in advance.
Best regards,
Felix Schwarz