Thanks for the logs. Is the problem only on Plex Web when seeking forward / backward ?
Would it be possible to get a 5 minute clip that reproduces the problem. Please indicate how to reproduce the issue.
I have noticed seeks in the log.
Does the issue arise with specific media files. One known issue is if there are no subtitles till sometime after video starts
You can produce a short clip of the mkv using tools such as mkvtoolnix. See https://support.plex.tv/articles/201035968-generating-sample-files-from-media/
