I'm in act 3 and no longer have the shielded condition, so it might just be a thing that the game forgets about after awhile. It sucks that your co-cop team didn't get to see that important info, but I don't think missing the shielded condition should affect you negatively going forward. I doubt the game even had any code to recognize missing that cutscene is possible.
(you can also get the cutscene going to the mountain path from the area near where Kithrak Voss was in act 1, but like others have said, Idk if you'll be able to trigger it after getting to the shadowlands).
