A script or two could be clogging your memory and causing it to crash.
Run your nwnx profiler and check the log to see what script(s) have been run the most times and/or used the most time.
I once had a weather system that never turned off once a player entered an area. It would continue to run with no players in the area. So, the more areas entered, the more weather checks. This caused the server to crash after about a day, as too many weather system checks got running.
So, I dissected the system and fixed it to turn off when playercount was 0 for the area. Since then, no more daily crashes.