Smush Pro, Version 3.3.2 with ‘Lazy Loading’ enabled doesn’t show images on pages generated by WP-Print ( https://wordpress.org/plugins/wp-print/ ), Version 2.58.1 even with WP-Print dropdown box setting ( WP Admin panel => Settings => Print ) named ‘Print Images’ set to ‘Yes’.
If ‘Lazy Loading’ within Smush Pro is disabled, images load without problems.
Suggested solution: in code, check if it’s possible to lazy load images on page, if not, do not change the image src code.