'Fixing' the background image of a div causes it to vanish?

Hello, forum!

I’m running into an issue where, if I make fixed the background image of the ‘Div Block 2’ element (first full-screen image of the skyline), it effectively dissapears in preview mode. This does not happen when the background image is NOT fixed – in this case, it displays as expected.

Can anyone lead me in the right direction as to what I’m missing/doing wrong?

Thank you very much for your help in advance!

Here is my site Read-Only: LINK