Trouble with background scaling

Hi there!
I love your theme, it works really great! So thanks!
I have an issue, where the background image of the “testimonials” and “about” section won’t scale to mobile devices.

I have really tried it all. But I have this theory that when the bootstrap grid reaches xs, it stops scaling the image or something.
Background: Cover, contain, inherit - nothing works.
Is it the grid that acts differently? the jumbotron image does scale, though…

Any tips?