@Shadex uhhh, what? The only content outside of the story quests itself that gates story progression is Explorations and you basically just do those in the order they're presented to you and that's it for unlocking story. There weren't ANY cutscenes that would've played if you were without friends or not, it's just not a thing that happens outside of the lobby, and running into cutscenes in the lobby is not the main method you're even meant to access them.
You can replay every single story cutscene and mission via the Story Quest menu, and in fact replaying the latter to get S ranks if you didn't the first time is a good source of SG. There's not much "uncovering" of story for a new player in PSO2 Global, and hasn't been on JP since Ep5 reworked the whole story progression.