Catacombs combing paths bug
I experienced the same bug one time I ran ASC by using the LFG-tool. We chose path 3 and suddenly Detha followed us even though noone chose path 2.
After doing some research I eventually found out that you had to die next to Detha and have her rez you (she will come automatically if you arent too far away) and die herself. After reviving her she will follow you and trigger the event to set up the traps.
The only loot you skip are the 26 silver and 20 tokens for completing path 2. Apart that you get the same loot as if you were completing path 2 and 3 alone.
I even heard about entire guilds abusing this bug on daily basis so a fix is needed.