I spotted this post from October and thought I would reference it as I am having exactly the same problem.
Ubuntu 16.04
Sabnzbd 2.3.1
Sonarr 2.0.0.5085
CIFS-Utils 2:6.4-1ubuntu1.1
Files appear to be ok and then often crap out halfway through watching.
Aside from debug logs, Is there anything I can try? I have no idea how long this has been going on and fear loads of files are now unusable.
Any help greatly appreciated. I’m at my wits end!
Link to other thread should be below.
Thanks!
Continuing the discussion from Episodes download but are corrupt when played back: