Monitor playback via Plex Dashboard → Now Playing. If needed, toggle the button on the top-right to expand the playback information.
Is the video and/or audio direct playing, direct streaming, or transcoding?
If your server cannot transcode in real time you will experience buffering.
Plex Web has limited capabilities due to web browser limitations. H.264 8-bit video will direct play. Most other video formats will transcode.
The Plex LG WebOS app also has limitations. Try playing the video without subtitles. Enabling PGS/VOBSUB/ASS subtitles results in a video transcode. If the audio is transcoding, enabling any subtitle results in a video transcode.
