Do not do the replicator node room if none of you you don't need it, bugs out the game (memory overflow) by the time you start the boss (specially if you start it but don't complete it), also when you get a plate maker key and put it in the middle DO NOT take it out, ever, leave it, kill the minotaurs and get the portal key and extra plate maker key and go to the proper side, afterwards you should be able to cap a plate, kill more minotaurs and get more keys, one for the other portal and the other plate maker key. Don't over dps the boss past mid health, when you dps in a second phase stop don't try to finish the boss let it go to middle and just shoot it's barrier maker node(s) to finish it. We we never intended to "go fast", go slow, do 2 phases and let it go to last stand. Bungie fumbled that whole thing hard they never fixed it like they never fixed Spire of the Stars post-release, they release content and forget about it because they're on a time crunch they're too busy working on the next shiny stuff.

Yes. These all could happen to some people and never happen to others. The weak spot of the shield to start the boss fight could not be destroyed. The weak spot could be destroyed but the boss would still be immune. If you damaged the boss to quickly, when it moved to the final phase it could be immune. If you took too long to damage the boss, it could be immune in the last phase. If you died in the boss room, your ghost might end up way outside of it with no way in. The puzzles wouldn't activate sometimes. This one was best handled by activating every Vex Conflux along the way. The door to the boss would usually open, but sometimes take several minutes just sitting in the last room.

Yeah best way I found it your solo is solo to boss room then use the legacy fireteam thing & title it encore boss kill, 2 join & you'll melt him easily.