PMS crashing after a few hours

i use a synology DS916+, latest DSM 6.1.5-15254,
and plex version 1.11.3.4803
my plex is crashing..meaning that it stop working..!
so if i try to stop it and relaunch.. it doesn't work.; it seems the only way is to restart my synology server
i attach the log.. maybe it is because of this error it stops functionning.