Unfortunately I don’t have time to really dig in to it as there’s a lot going on there, but a common cause for this is animations that start offscreen. If you have any instances of this, check whether the parent element is set to show or hide overflow - that could solve it.
As an aside, I’m only seeing superfluous space at a viewport width of 300px or below - that seems to contrast with the screenshot you included. Have you managed to partially resolve this since posting?