Against the Corruption
I’m having issues with that same quest right now. I really dread these personal story quests all together! I love everything else about the game but these always seem to cost me way to much coin.
I have finally found a way to prevent the ambush, which is to kill all mobs around the area including the Abomination at the tomb entrance, and also by leaving the Plaguebearer as the last monster to kill along the path. I only escorted the npcs after the mobs were cleared and yep, there was no more ambushes.
Wtf PS difficulties.