I tried switching to official plex docker from the linux repo one and what finally fixed my issues was stopping the docker then going to /mnt/cache/appdata/plex/Library/Application\ Support/Plex\ Media\ Server/Codecs/ and deleted the 2 files out of the codecs. Then I restarted the docker and it redownloaded the codecs and bam everything is FINALLY working. Didn't have to revert the plex versions from the latest. Tested on both dockers with success.