Plex Media Server downloads the codecs it needs when the need arises. It also downloads previously used codecs when updating versions of Plex Media Server
If there is a problem with this automatic download mechanism then it needs to be investigated and that can only be through following the support articles
https://support.plex.tv/articles/201643703-reporting-issues-with-plex-media-server/
https://support.plex.tv/articles/200250417-plex-media-server-log-files/
If your problem is not when using the Plex App for LG then of course this does not apply
