It's a faction problem. NWN is infamous for those.

The way NWN works is that every creature in the game is assigned a faction. Some of these are friendly to one another, some are neutral, some are hostile. However, if a creature attacks something from a faction neutral to them, the entire faction will (usually) go hostile. This happens even if they accidentally damage one another.

This is why if you accidentally (or deliberately) attack an NPC, some others will go hostile, but some won't.

During development, this caused some hilarious problems for the designers. Like the Mystery of the Disappearing Orcs that was described in a gamasutra post-mortem. This was a bug where playtesters would enter an area with an orc camp, only to find it completely empty. There would just be a few bags of "remains" laying on the floor. The orcs had all died somehow, but the devs were stumped how that had happened.

Turns out it was the deer.

Deer belong to the animal faction. In an earlier area, an orc Shaman had hit an animal with a spell, turning the animal faction hostile to the orcs. Meanwhile, at the camp, there was a spawn point that would create a deer whenever there were none in the area. So, a deer would spawn, and because of the faction issue, it would attack the orcs. The orcs would immediately kill it. But another deer would spawn indefinitely. So whilst the playtesters would be playing for hours, the Orcs would be facing an infinite horde of deer suicide attackers. And eventually, through sheer luck, the orcs would be worn down. By the time the players got there, all signs of the epic battle had disappeared, and there was just the last deer wandering around.

Now, fixing faction problems is rather tricky, as a player. (DMs can do it if they have the right tools and scripts.) If a faction is hostile to the player, you can usually fix it by getting killed and then respawning. But if NPCs are attacking one another...

Well, one thing you can do is enable debugmode (hit ~ and type "DebugMode 1" without quotes.) and then hit the period key. "." That will bring up a debug menu listing all areas in the module. Double click the area you're in, double click on "creatures" and select the hostile NPC. Then find the button that says "toggle AI" somewhere at the top of the window and click that. Finally, select the attacking NPC again and use the "move" command to move her away from the jester. That should stop her from attacking. You can them move her back.

You can then hopefully continue the game as usual, but when the battle begins, it may be that Sabal will just stand there doing nothing because of the disabled AI. So you'd better repeat all these steps to toggle the AI back on when you're done.

Honestly, it's a big hassle, and reloading an earlier save game like you did is usually a better and more reliable solution. Still, it's useful to know how the debug mode and area console work. You can use it to fix a lot of bugs you encounter, which is particularly prevalent in custom modules. (Not even necessarily because the modders left bugs in, but because NWN scripts tend to break down when there's a lot going on at once.)

Oh, and always remember to turn debugmode off again (~, DebugMode 0) or you might run into other issues.