Ok, i've had this problem for last 2 versions and i haven't received any specific descriptions on this bug.
Back when Kirei was hosting, she had a "theory" that it was caused by the Byond itself when the server was up for too long.
Since NC has SO many NPCs (dungeon), it overloads Byond after a long time of hosting without a reboot.
So here is what ill do then, I will make the server auto reboot every 3 hour and 30 minutes. This way, when u have the first chuunin, you have the chance to finish it in 30 minutes and then it will reboot so that the server gets refreshed once in a while...
Note: Mayb this is why other naruto games have auto-reboot lol Until now, i didnt feel the need to do so... but now i will.