@asyag thanks for your reply
I investigated the problem, at the following link you can find the page (of the website under development) that does not display the images.
https://tecnoloweb.ovh/zoccolimania/?product=zoccoli-rossi-tacco-12-kiara-shoes-2
In the following link you can find the page of the official website where I worked around the problem by disabling the javascript merge from the WP-Optimize 3.1.6 plugin
https://www.zoccolimania.it/negozio-sandali-donna/zoccoli/zoccoli-rossi-tacco-12-kiara-shoes-2
Wordpress 5.6 and Photo Gallery 1.5.66 for both websites
Best regards
