[/share/CACHEDEV1_DATA/.qpkg/PlexMediaServer/Library/Plex Media Server/Codecs] # ls
2584b51-4483-linux-x86_64/
[/share/CACHEDEV1_DATA/.qpkg/PlexMediaServer/Library/Plex Media Server/Codecs] # cd 2584b51-4483-linux-x86_64/
[/share/CACHEDEV1_DATA/.qpkg/PlexMediaServer/Library/Plex Media Server/Codecs/2584b51-4483-linux-x86_64] # ls
libaac_decoder.so libac3_decoder.so libh264_decoder.so liblibx264_encoder.so libvc1_decoder.so
libaac_encoder.so libdca_decoder.so libhevc_decoder.so libmpeg4_decoder.so
The real key is this line: HTTP error requesting GET https://downloads.plex.tv/codecs/2584b51-4483/linux-x86_64-standard/libh264_decoder.so (35, SSL connect error) (OpenSSL SSL_connect: Connection reset by peer in connection to downloads.plex.tv:443 )
This typically means the client got a bad certificate which is often due to a proxy or filewall blocking this site. Could that be the case in your network setup?