19th Anniversary "Lost but Not Forgotten" cant find Sila Warren.

We had cleared the room, but were under the impression the Presence becomes passive/untargetable while adds are up. So our mistake probably was to switch to adds as they popped. When we realized the red con kept beating the tank it was too late. When we came back, the boss had reset but adds were still up, at which point half the group lost their heart unfortunately. Maybe we just underestimated the encounter, as getting there was pretty straightforward. Guess better to fail this than the final fight, I guess?

Sad the mission basically excludes pug's due to it's design (unable to replace players that leave because mission locks on request, adds not despawning if you fail the ghost punishes groups that try to learn the encounter), because up to that point for me it was one of the best dungeon crawls ever. But convincing others to take on a 2+ hours trip when only one person gets the reward isn't going to happen very often. Even if the event in itself is fun to play.

We did fine right up until the last room with Harris, The ghosts were pretty hairy but we burned name and dotted up trash finishing them after it died. Harris plus adds and their nasty dots ate our lunch.
Run back rez/recover.
The adds can be root/snared and are not agro linked to Harris, they are either highly resistant or immune to mez/stun from enchanter. You can range pull them with a no damage effect (they will summon once damaged). Did not notice nor care if Harris could be root/snared.

Back up a couple rooms select a good spot to set up group with working room for puller. Druid pulled adds with snare and beam rooted then off rooted while tank picked them off with agro tools and crew blew them down one by one. Druid was self healing the dots from the pack and avoiding melee.
We got it down to just Harris and one add hiding behind pillar, they are not leashed to room so we dragged them back to crew splitting off the add and killing Harris first.
So either a druid/ranger with beam root, or possibly a wizard with their ae root and snares would work to control the adds.Have to have a non damage ae root/snare option for it to work as they move way to fast to chain single them and once damaged you would get ping ponged all around room while they dotted you to death.
Or go with the old classic monk/SK single pull.