one element has a fixed width, or induced width larger than the viewport
one element has an interaction that makes it sit outside the viewport, hence enlarging the width of the page
To fix it:
locate the section where it happens: to do so, delete sections one after another and check the bug after each delete.
In your case, when I delete Home top section it almost fixes it. So we have an issuer there and in another section
Deleting Home Middle section fixes it entirely so we have an issue there too.
So, all your aaa bbb etc elements have plenty of positionning value, especially left and right, that make them go out of the viewport. You need to remove all those and use padding on the parent for your layout