i tried reproducing the trick but i was not successful. When am i supposed to go back to an offline lobby? After i start an online lobby the cutsccene does start but the menu goes away after the dialogue starts. If i switch back to an offline lobby after the cutscene starts, before the dialogue, and close the menu manually it progresses as normal.

i figured out why some of the cutscenes won't start, it's when your part is attacking an enemy. I usually had it happen when i faced zaria in upper raven's rill or when i picked up the 1st book in the grand chapterhouse. It was just my companion attacking the skeletons or the sentinels. Another "glitch" i found out is if your fps is too high you cannot move anymore. This i think happens if the fps is above 300, i noticed it in the causeways but i'm guessing it will happen anywhere if you can get that much fps

oh there is also this but i personally never encountered it. You would just reset if this were to happen in a speedrun anyway

sometimes some of the cutscenes won't start immediately and give you a long and annoying black screen. I am not 100% sure why that happens and how to avoid it. Another one i can think of is you can avoid/delay the level up prompt by holding the dodge key even if you are not in combat. Not sure why you would do that but yeah.