Blog feed images broken

Hi there

This may be an issue a lot of people are experiencing right now but the images in my blog feed have become broken. I fixed this issue yesterday by restoring a backup but it’s happened again.

I thought it might have something to do with my trying to add code to the functions.php file, but maybe this is unrelated? I did add the following code to the bottom of the functions.php and it did work but every time the next day the code has changed and my images are broken!

Any ideas how to fix this?

/**--------------------------------------------------------------------------------
# Category Image
---------------------------------------------------------------------------------*/

function prefix_page_header_background() {
    $css = '';
    $image = z_taxonomy_image_url();
    if ( is_category() ) {
        if ( function_exists('z_taxonomy_image_url') ) {
            $css = 'header.page-header {
    background-image: linear-gradient(to right bottom, rgba(0, 0, 0, 0.6), rgba(0, 0, 0, 0.6) ), url(' . $image . ') !important;
    background-position: center;
    background-repeat: no-repeat;
    background-size: cover;
    }';
        }
    }
    echo '<style type="text/css">' . $css . '</style>';
  }
add_action( 'wp_head', 'prefix_page_header_background' );

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