version 5

After submitting my first reply there was no confirmation by this – so sorry, if you see two responses.

First of all, Photoswipe 5 works fine in general – also see here: https://wordpress-demo.arnowelzel.de/lightbox-with-photoswipe-5/

Also the link you added does not show pictures for a lightbox, only to articles. And on one of the article pages I saw another lightbox – propably provided by the gallery you use.

Avoid “optimization” of JavaScript – this does not work with Photoswipe 5 since it uses modules which don’t work with additional “optimization” into one single JavsScript file.