Yup same issue. Had to bring 10 ppl and nuke the whole place at once to clear 200+ spawned ghosts. So far encountered 4 places like this in endgame and 2 of them are almost impossible
There are at least 3 quest lines in Reekwater where this can happen. If someone triggers the part of the quest that has waves of mobs that spawn, but then dies, the mobs do not reset. They will then continue to trigger additional waves as would normally happen when killed. This often causes stacks of these quest mobs to remain in the area, making the quests almost impossible to do.
The same effect can also happen if multiple people doing the quest all trigger the wave spawning event at the same time. Each player will trigger their own set of mobs, leading to nearly instant death as the group gets swarmed.