I have a similar problem! Background images suddenly don't get displayed anymore.
It only gets displayed when I activate an Image Effect for the background image. For the moment I did that to fix it. I used Film Grain but I put everything to zero without animation because this way it looks like a normal image without any effect.
My main site where I used the grain effect now to fix the problem: https://groundofaces.com/
A 2nd older version of the same site where I didn't change anything and now suddenly the background images don't get displayed: https://www.groundofaces.com/airbase
But in general, it seems to have loading issue and also seems to have changed the height of the sections. We didn't change anything on the site the last few days.