The print trigger on the page you linked to above is targeting an element with a class of printplease. The item you are targeting is:
<img class="aligncenter size-large wp-image-27537 printplease print-me hidden" src="data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%201024%20558'%3E%3C/svg%3E" alt="$3 coupon for Kent product" width="1024" height="558" title="$3 coupon for Kent product" data-lazy-src="https://2yxycb1azbei20xsf81f831w-wpengine.netdna-ssl.com/wp-content/uploads/sites/4/905244-3-OFF-KENT_BOT_2250.jpg">
For troubleshooting you will want to turn off the close after print in the plugin settings.
1. is the image being loaded, but is just being hidden in css?
2. is the image not being loaded due to lazy-load?
3. is enough time being provided for the image to fully load before the print is triggered?
Please provide a link to a coupon that is correctly printing and maybe we can see something that is obvious from the source.
Thank you for the suggestions… It was #2 in your questions; lazy load was enabled. Fixed now!