Ok I found out that it is a bug only for images with space in the name, e.g. abc.jpg
works fine but a b c.jpg
doesn't work after publication when put as a bg image
I will fix this soon, but as a workaround you can remove the spaces in the image names or add your images with an image block instead as a bg image
I'll keep you posted when it is fixed
PS: I will ask you to test new versions on canary.silex.me soon, this is important to avoid such problems in production, thx