Hi Michael, are you saying it does not work on iPhone/Pad only? Looking at your site on Android it works fine… because I have no iDevice to test with, I tried your site on online services like https://appetize.io/ and https://app.testobject.com where a real iPhone 5 is used, and all show the light box working from the sliders but not from the galleries. I also tested on an Android phone and there the same thing happens.
But as soon as I ask the browser to get the “Desktop version”, all gallery images can be loaded in the light box.
Do you know if there are options in the Envira settings that tell it to behave different on mobile devices? Or are you using another plugin that creates different versions of your site for different devices, like the Jetpack Mobile Theme module?
Slightly related, not requested but well meant advise: you might want to look into a way to reduce the current 20+ Mb that is downloaded upon first page request because not many mobile visitors will like that. Maybe split the different galleries over different pages?