I am not able to play back any video files using the Plex app with or without direct play.
I have to use an external player (MX Player).
I see the following two lines in Plex Media Server.log whenever I try to play any video file with the built in player.
Sep 22, 2016 19:21:21.435 [0x7ff43fbff700] ERROR - Missing X-Plex-Session-Identifier and X-Plex-Client-Identifier header
Sep 22, 2016 19:21:33.727 [0x7ff42cfff700] WARN - Got a request to stop a transcode session without a session GUID (or with an invalid one).
I am using Plex Media Server 1.2.0.2765 on Linux.