Image attachments throwing error in new WP migration

I have a WP site that works fine in my testing environment. I migrated to a sub-directory on the clients server and now I’m having an issue with image attachments.

Fist of all, when I go to the media library, the images are all there, but the thumbnails are not showing, instead, they’re replaced with a file icon. See screenshot-1 below.

Secondly, when I try to view the attachment page I’m getting the following errors:

Warning: Illegal string offset ‘width’ in /xxx/image.php on line 28

Warning: Illegal string offset ‘height’ in /xxx/image.php on line 29

Here’s the code in the image.php file that is creating the issue:

$metadata = wp_get_attachment_metadata();
printf( __( 'Published <span class="entry-date"><time class="entry-date" datetime="%1$s" pubdate>%2$s</time></span> at <a href="%3$s" title="Link to full-size image">%4$s &times; %5$s</a> in <a href="%6$s" title="Return to %7$s" rel="gallery">%7$s</a>', 'detund' ),
    esc_attr( get_the_date( 'c' ) ),
    esc_html( get_the_date() ),
    wp_get_attachment_url(),
    $metadata['width'],
    $metadata['height'],
    get_permalink( $post->post_parent ),
    get_the_title( $post->post_parent )
);

Specifically, the $metadata['width'] and $metadata['height'] sections.

Because of this, functions like WP’s featured image, are not working.

Has anyone come across this before, or can anyone offer a solution for this issue?

As always, any help is greatly appreciated. Thanks!