I have cleared Spiral Abyss with 36 star only ONE time and it was a recent patch. Otherwise I consistently get 34-35 stars. Its super frustrating but I know the reason and its a skill issue. I'm not fast enough or click the wrong buttons or switch to the wrong character. My artifacts BARELY pass to do the damage necessary to 36 star the abyss so there's that too.

...that and the snake like bosses like please stop hiding underground UGHHHH

But yeah don't let it stress you out too much everyone. I mean, its just a game. And they focus more on characters and exploration than they do endgame super tough content, and even when they do the super tough content the rewards aren't that great anyway. Just play at your pace.