Your logs show that user plex does not have permission to the video share.
Please recheck it.
I will also ask if you rebooted DSM as the PMS 1.15.4.994 notice stated.
Your logs show:
Aug 09, 2019 11:06:07.804 [0x7f78997fa700] ERROR - Unable to find title for item of type 5
Aug 09, 2019 11:06:07.804 [0x7f78997fa700] DEBUG - MDE: analyzing media item -1
Aug 09, 2019 11:06:07.804 [0x7f78997fa700] DEBUG - MDE: : no direct play video profile exists for http/mpegts/
Aug 09, 2019 11:06:07.804 [0x7f78997fa700] DEBUG - MDE: : no direct play video profile exists for http/mpegts//
Aug 09, 2019 11:06:07.805 [0x7f78997fa700] DEBUG - MDE: : codec is unavailable for analysis
Aug 09, 2019 11:06:07.805 [0x7f78997fa700] DEBUG - MDE: : codec is unavailable for analysis
Aug 09, 2019 11:06:07.805 [0x7f78997fa700] ERROR - Unable to find title for item of type 5
Aug 09, 2019 11:06:07.805 [0x7f78997fa700] DEBUG - MDE: : selected media 0 / -1
Aug 09, 2019 11:06:07.805 [0x7f78997fa700] DEBUG - Cleaning directory for session 25a5fbdb-a4a6-49a8-92c6-a0fd14893249 ()
Aug 09, 2019 11:06:07.805 [0x7f78997fa700] DEBUG - Starting a transcode session 25a5fbdb-a4a6-49a8-92c6-a0fd14893249 at offset -1.0 (state=3)
Aug 09, 2019 11:06:07.805 [0x7f78997fa700] DEBUG - Streaming Resource: Added session 0x7f7864615320:25a5fbdb-a4a6-49a8-92c6-a0fd14893249
Aug 09, 2019 11:06:07.806 [0x7f78997fa700] DEBUG - TPU: hardware transcoding: enabled, but no hardware decode accelerator found
Aug 09, 2019 11:06:07.806 [0x7f78997fa700] DEBUG - TPU: hardware transcoding: final decoder: , final encoder:
The video share is also owned by Video Station. It is highly recommended you create your own shares and move the media to them (out of the Synology pre-defined share).
Any DSM or Synology app updates can and often do impact the video share.
If you need assistance in moving your media without losing metadata or watch history, please let me know.
