This issue sounds quite similar to what I had with iOS client where video virtually stops or getting a very long delay after one or two clicks of forward seeking and it only happens with “Direct Streaming” with soft subtitles turned on.
https://forums.plex.tv/t/ios-app-seeking-broken-when-smi-or-srt-subtitle-turned-on/
The only solution I found until now is to make it “Direct Play” by turning off subtitles or switch to experimental player avoids “Direct Streaming” which is required for side-loading soft subtitles for the default player. The new player recently came out of beta and became an official feature, but it still fails with the very same seeking issue when it has to go down with “Direct Streaming”, for example, in the case of side-loading SMI subtitles which is somehow not supported by the new player (SRT/ASS works fine).
One thing I noted at the time was that whenever a seek request triggered by the client, the server always started transcoding (merely for merging soft subtitles into HLS streams, not for full video transcoding) from the beginning, wiping out any on-going/already processed segments. It seemingly made any seeking attempts far from the beginning of the stream very inefficient as play was progressing and also added up much more burden when transcoding was interrupted by another seeking request.
A funny thing was that if I made it full video transcoding instead of subtitle-only transcoding, the problem went away and everything seemed to work fine again, except degraded video quality of course…
Not sure if this issue is still relevant nor has something to do with WebOS whatsoever, just wanted to chime in as someone used to try hard on LG device, but finally had to give up due to some never fixed issues:
https://forums.plex.tv/t/fix-settings-forgetting-bug-on-lg-smart-tv-with-webos/
https://forums.plex.tv/t/plex-is-unable-to-start-due-to-an-error/
