I have this same issue. I don't know what triggers these scenes, but I too assumed it's long rest. I don't rest often when I play. I didn't rest in other BG games until the party were actually falling over from exhaustion. In BG3 the party said they were tired, but there weren't any negative status effects so I figured they could push on awhile. I got the Raphael scene, and a couple Astarion scenes and eventually the dream. Then I went through the whole goblin camp without a long rest. By the time I did rest it was the tiefling celebration and I hardly knew my party members so they hadn't much to say. Next rest, Gale had a big scene revealing the secret inside him. It was AFTER that upon a later rest that Gale asked for a magical artifact, hinting that there was a secret. But he'd already told me the secret! So I think the scenes happened out of order.
It didn't occur to me that the dream could be triggered by using the Illithid power. But that also requires rest, so I didn't use it often and got the special power much, much later than maybe I should have. The first time you use the power the narrator says something about losing something important, which made me think of Prey where using the powers resulted in you becoming more of a monster. Since I could avoid it in favor of other choices, I did.
Do the scenes happen based on their opinion of you? If so, they should've been triggering because you get approval/disapproval even when they aren't with you.
If the scenes, instead, happen based on the plotline, then something seems to be out of order with Gale's scenes. I also haven't had anything eventful happen at camp with Wyll, Shadowheart, or Laezel, unless those are post Underdark. I've been resting a lot more to see what I've missed, but nothing has been occurring.
But I kind of agree with OP about there being some kind of barrier for the goblin camp since finishing it results in all other cutscenes being blocked in favor of the tiefling celebration. I feel like I did the camp too soon and confused Gale.
