Scroll into view backgrounds not working

While scrolling into view once works fine on my backgrounds, if I try to scroll into view again, the interaction no longer seems to work.

I can scroll once, the background on each section changes color as expected. If I scroll back, either up or down, it no longer works. Any suggestions?

Background Scroll Interaction tutorial I’m using
My site’s read-only LINK. The interaction

@PixelGeek I based this on your tutorial, perhaps you can tell what’s missing?

Thanks all for your suggestions!

Here is my public share link: LINK