Unofficial Skyrim Special Edition Patch

#Mod_Priority,#Mod_Status,#Mod_Name,#Nexus_ID
"0000","+","DLC: HearthFires",-1
"0001","+","DLC: Dragonborn",-1
"0002","+","DLC: Dawnguard",-1
"0003","+","Enable 1st Person For Werewolf and Vampire Lord SSE",27513
"0004","+","Kalilies Brows",40595
"0005","+","SkyUI",12604
"0006","+","RaceMenu",19080
"0007","+","Cloaks of Skyrim SSE",6369
"0008","+","Unofficial Skyrim Special Edition Patch",266
"0009","+","Stones of Barenziah Quest Markers",684
"0010","+","Unread Books Glow SSE",1296
"0011","-","Improved Camera",0
"0012","+","Amazing Follower Tweaks SE",6656
"0013","+","KS Hairdos SSE",6817
"0014","+","Breezehome",2829
"0015","+","Ethereal Elven Overhaul",24273
"0016","+","Ethereal Elven Overhaul patches for SSE",7351
"0017","-","Immersive Citizens - AI Overhaul",173
"0018","+","Cutting Room Floor - SSE",276
"0019","+","Anna NPCs SSE",1163
"0020","+","Touring Carriages",15948
"0021","+","Static Mesh Improvement Mod",659
"0022","+","INIGO",1461
"0023","+","Point The Way",352
"0024","+","Aurlyn Dawnstone - The Reclusive Philosopher",9536
"0025","-","Improved Eyes Skyrim",9141
"0026","-","A Guiding Light - Clairvoyance Reimagined",35464
"0027","+","All in one",32444
"0028","+","SSE Display Tweaks",34705
"0029","+","Glowing Ore Veins 300 SSE",9147
"0030","+","A Quality World Map",5804
"0031","+","SSE Engine Fixes (skse64 plugin)",17230
"0032","+","Better Wooden Mask - Bromjunaar Treasury",23541
"0033","+","SkyUI SE - Flashing Savegames Fix",20406

This issue has been reported numerous times over the years, but none of us on the project team have ever experienced it in our own games. There was a fix done in the patch to attempt to address the issue that extended the radius of the trigger box near the gate with the pull chain (see Issue #18354). We suspect that the only way the problem could still occur is due to a mod conflict (more specifically a follower mod). Amazing Follower Tweaks is one mod that can apparently cause the quest to break because it overrides the game's follower restrictions. Nightingale Hall is one of the locations in the game where you aren't allowed to bring a follower with you.

FWIW, we made all of our followers stay at the beginning of the dungeon and Karliah still walked away later on.

You need to go back and try this again and leave all of the followers OUTSIDE of the dungeon. Once you're inside, it's too late. The possibility exists that you're simply bringing in too many people and that's why Bethesda wrote the follower restrictions in that they did.

Given the lack of additional feedback and the load order containing a number of follower related mods, we're going to close this one as a mod conflict.