In looking through your logs:
Small permission problem with: Jan 21, 2017 21:07:23.335 [0x7f73fabff700] ERROR - [Notify] Failed to add watch for /mnt/share/movies/Keanu (2016) (13: Permission denied)
I would like you to check for the existence of the AAC decoder and encoder in "/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Codecs/c9ea179-1157-linux-ubuntu-x86_64/"
The log file indicates the file is too short. Either incomplete download (you have internet “404” errors in other areas of your logs) or damaged file.
In the codecs directory, you should find both aac encoder and decoder. Please do the following.
cd "/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Codecs/c9ea179-1157-linux-ubuntu-x86_64/"
ls -la
sudo systemctl stop plexmediaserver
sudo rm -f libaac*
sudo systemctl start plexmediaserver
Leave this terminal window open. We will use it to monitor progress.
Now return to the movie you’re having difficulty with. Analyse it again. When it’s complete, do ls -la in the Codecs directory again. You should find both libaac files present (decoder and encoder).
It should look something like this (dependent on your media)
-rw-r--r-- 1 plex plex 433752 Jan 18 15:43 libaac_decoder.so
-rw-r--r-- 1 plex plex 354680 Jan 18 15:42 libaac_encoder.so
-rw-r--r-- 1 plex plex 301256 Jan 18 15:42 libac3_decoder.so
-rw-r--r-- 1 plex plex 292104 Jan 18 15:42 libac3_encoder.so
-rw-r--r-- 1 plex plex 435880 Jan 18 15:42 libdca_decoder.so
-rw-r--r-- 1 plex plex 586216 Jan 18 15:42 libflv_decoder.so
-rw-r--r-- 1 plex plex 1378376 Jan 18 15:43 libh264_decoder.so
-rw-r--r-- 1 plex plex 1086408 Jan 18 15:42 libhevc_decoder.so
-rw-r--r-- 1 plex plex 1270152 Jan 18 15:42 liblibx264_encoder.so
-rw-r--r-- 1 plex plex 487944 Jan 18 15:42 libmpeg1video_decoder.so
-rw-r--r-- 1 plex plex 484008 Jan 18 15:43 libmpeg2video_decoder.so
-rw-r--r-- 1 plex plex 683496 Jan 18 15:42 libmpeg4_decoder.so
-rw-r--r-- 1 plex plex 629432 Jan 18 15:42 libmsmpeg4v3_decoder.so
-rw-r--r-- 1 plex plex 909784 Jan 18 15:43 libvc1_decoder.so
-rw-r--r-- 1 plex plex 629432 Jan 18 15:42 libwmv1_decoder.so
-rw-r--r-- 1 plex plex 673112 Jan 18 15:42 libwmv2_decoder.so
-rw-r--r-- 1 plex plex 909784 Jan 18 15:42 libwmv3_decoder.so
[chuck@lizum c9ea179-1157-linux-ubuntu-x86_64.181]$
Please let me know if your findings differ substantially from mine and/or do not resolve the issue.
