This is quite ridiculous,
We understand that the issue at hand is the exploitation of the feature in the NPC Highest Quest Manager, but why is it that because of a small number of cheaters who abuse this feature, most innocent players are inconvenienced and lose access to enjoying the game's mechanics?
I'm not making empty complaints and am trying to contribute some thoughts that I think of (at least I'm TRYING TO THINK).
1. Improve your server's security; we, as ordinary people, don't understand how to do it, and if you as developers can't figure it out either, I can only laugh.
2. Manual approach: Maintain the NPC with a dedicated person in charge who stands by on a schedule (office hour); if unusual activity is detected, terminate the activity! Outside of staff working hours, please disable the NPC feature (this may sound ridiculous, but it's a fair way for other players).
These are some thoughts that, in my opinion, are quite clear, and I kindly request you to reconsider the WELL-BEING OF YOUR PLAYERS.