The dunPOIReachForswornRaidQST quest is about two soldiers attacking a small Forsworn camp.
https://elderscrolls.fandom.com/wiki/Forsworn_Camp:_Reachwater_River

The quest/event is supposed to start when you get near the camp and should stop when you go away.
Usually it starts when you walk along the road minding your own business and don't even notice the not-so-visible place, and of course you have no idea that something has started behind your back.

Sometimes (often, in my game) the script dunPOISoldiersRaidOnStart doesn't stop looping and stays active in the save game, and the  dunPOIReachForswornRaidQST quest keeps running.
While the original script and quest look fine and should work as intended, for some reason they not always do.

Another smaller issue I noticed: If you leave the camp and the cell unloads, and then you get back while the Forsworn are dead or not-yet-respawned, two new soldiers pop up and stand there like idiots.
This has been taken care of, too.

If you're not starting a new game, you should install this while away from the Reach.
Then (again, if you're not starting a new game with the fix already installed) approach the camp at least once (when you happen to be there, no hurry) so that you see the soldiers spawn and start fighting. This is because I don't want to add extra code just to check and auto-stop the quest -- it would be redundant when starting a new game or for those who don't have the quest stuck.

After that you might still have a surplus of soldiers, survivors from previously-botched events.
If there are any, you can select them in the console and -- after making sure that their ID begins with FF -- enter MarkForDelete.
Or leave them alone; I suppose they'll die sooner or later -- everyone does.