WordPress Multisite header img src is lost from staging to production

Question

I'm working on a Multisite where each site has its own header image. I have a staging and production setup where everything is edited on staging. A new site gets created and it has its own header image, all good.

But when I go to move to production, doing a staging database file export, changing the domain names for production, and then importing that database file to the production server those header images are missing.

In the WP-Admin it sees the Previously uploaded image and the src is empty. I get img src="" on inspection of the element.

Anyone else have this experience or something similar? In my functions.php I've added custom-header theme support.

// Add custom header support
add_theme_support( 'custom-header' );

This might be where I'm going wrong but I also have this in the custom-header.php

function my_network_custom_header_setup() {
add_theme_support( 'custom-header', apply_filters( 'my_network_custom_header_args', array(
    'default-image'          => 'http://mynetwork.com/wp-content/uploads/my-logo-default.png',
    'default-text-color'     => '000000',
    'width'                  => 736,
    'height'                 => 220,
    'flex-height'            => true,
    'wp-head-callback'       => 'my_network_header_style',
 )));
}
add_action( 'after_setup_theme', 'my_network_custom_header_setup' );

I recently added a default image so at least the page doesn't look broken and that works.

Any suggestions for how debug this issue? Maybe it's my callback that's missing something.