Hey there's a bug for the level 0 scroll. Change line 120 to

let level0 = document.querySelectorAll('img[src="//d35aaqx5ub95lt.cloudfront.net/images/crowns/fafe27c9c1efa486f49f87a3d691a66e.svg"]');

nice. Thank you, I couldn't work on my scripts for a longer time.
I'm curious, how the script works at your browser. I've experienced that the new Duo tree update function breaks the script, because it only loads the lessons in the visible area. If you're not experiencing the same I would be happy to hear about what browser do you use and what scripts, so I can look into it to find a solution.
Best regards

I've rewritten the script completely so this isn't a bug any more.