I can tell you what we did but I don't think it will help. Our LS members couldn't get back in the other room. I think its random because on our first run we got there by complete luck.

(at this point we had 6 mins left, took 40 mins to figure out how to not get sent back to the start). When we warped to the room with 3 circles, we took the bottom one instead of the NW, NE circles and it took us to an a room like a backwards "L" We didn't make it to the boss but we did see the cut scene