Alright, so it was because of the fixed background CSS I added. Unfortunately, that CSS was in place for a reason. The parallax effect doesn't work the same with the new sections. I don't understand fully, but it only works by making the background image larger than it should be. I was told the only way to fix this was with that code.
In the classic sections, I simply activate parallax and it works fine. How can I achieve the same parallax effect as the classic section while using the new style?
I've made an example page showing both examples. The new section is the top one, in order for there to be any parallax at all, the image must be much larger (and distorted as a result). The lower one is classic, it works perfectly fine. The fixed background happens automatically and parallaxes without resizing.
This is the code I was using: