Blood Relations, it's called. When it gets to the point "investigate the sound", the arrow points at nothing interactable. Nothing in the room is, in fact, interactive. So progression ends there.
Reset dungeon and it that doesnt work reset quest aswell, repeat if necessary.
I dont remember what part of the quest that is but make sure that the NPC are following you through the entire dungeon.
This was a known issue since long, and it still exits, looks like Zenimax doesn't give a crap and will make people remake the dungeon and waste like 30 minutes every time till they are lucky.
I tried completing Blood Relations quest 2 times with different groups, but still it gets bugged after the 2nd boss battle (spider waves). Also killed all the bosses including the end-boss, npc's were all talking but didn't get the skill point, also i got the achievement for speed run although the quest tracker shows otherwise. It happened to everyone in the group.This is annoying.
This is a bug that we are actively investigating. It appears to happen when the followers for the quest get stuck at a certain point. When you next experience the bug, please be sure to submit a /bug report, as it contains valuable information about your character that can help us investigate the issue more swiftly. Thanks for your patience and for the reports!
I got stuck at Search for Ata'var. There's no interactable NPC in the marked area. Group member said she did it 4-5 times already, everytime the same bug.