I cannot get any lightbox working with the Justified Image Grid plugin. I haven’t tried any other grid or lightbox combos.
Things I have tried:
* Firefox, Brave
* Every relevant option in the plugin
* Multiple jquery versions (in the plugin options) which definitely do load
* Checking that there is only one jquery.js loading in the network tab
* Resetting all the theme (Avada) options
* A totally different theme
* Disabling every single plugin, except JIG
* Renaming my .htaccess
* Setting it up on a similar WordPress install where it works out of the box!
This is what I get in the console on page load:
jquery.min.js?ver=3.7.1:2 jQuery.Deferred exception: $(…).JIGphotoSwipe is not a function TypeError: $(…).JIGphotoSwipe is not a function
at window.jigAddLightbox1 (https://mydomain.com/:85:258)
at f (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:29335)
at a.createGallery (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:24358)
at a.init (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:17852)
at new e.justifiedImageGrid (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:57366)
at HTMLDivElement.<anonymous> (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:57493)
at Function.each (https://mydomain.com/wp-includes/js/jquery/jquery.min.js?ver=3.7.1:2:3129)
at ce.fn.init.each (https://mydomain.com/wp-includes/js/jquery/jquery.min.js?ver=3.7.1:2:1594)
at e.fn.justifiedImageGrid (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:57422)
at initJIG (https://mydomain.com/:85:502) undefined
ce.Deferred.exceptionHook @ jquery.min.js?ver=3.7.1:2
t @ jquery.min.js?ver=3.7.1:2
setTimeout (async)
(anonymous) @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
fire @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
ready @ jquery.min.js?ver=3.7.1:2
P @ jquery.min.js?ver=3.7.1:2
jquery.min.js?ver=3.7.1:2 jQuery.Deferred exception: $(…).JIGphotoSwipe is not a function TypeError: $(…).JIGphotoSwipe is not a function
at window.jigAddLightbox1 (https://mydomain.com/:92:258)
at f (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:29335)
at a.createGallery (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:24358)
at a.init (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:17852)
at new e.justifiedImageGrid (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:57366)
at HTMLDivElement.<anonymous> (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:57493)
at Function.each (https://mydomain.com/wp-includes/js/jquery/jquery.min.js?ver=3.7.1:2:3129)
at ce.fn.init.each (https://mydomain.com/wp-includes/js/jquery/jquery.min.js?ver=3.7.1:2:1594)
at e.fn.justifiedImageGrid (https://mydomain.com/wp-content/plugins/justified-image-grid/js/justified-image-grid.min.js?ver=4.5:1:57422)
at initJIG (https://mydomain.com/:92:502) undefined
ce.Deferred.exceptionHook @ jquery.min.js?ver=3.7.1:2
t @ jquery.min.js?ver=3.7.1:2
setTimeout (async)
(anonymous) @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
fire @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
ready @ jquery.min.js?ver=3.7.1:2
P @ jquery.min.js?ver=3.7.1:2
jquery.min.js?ver=3.7.1:2 Uncaught TypeError: $(…).JIGphotoSwipe is not a function
at window.jigAddLightbox1 ((index):85:258)
at f (justified-image-grid.min.js?ver=4.5:1:29335)
at a.createGallery (justified-image-grid.min.js?ver=4.5:1:24358)
at a.init (justified-image-grid.min.js?ver=4.5:1:17852)
at new e.justifiedImageGrid (justified-image-grid.min.js?ver=4.5:1:57366)
at HTMLDivElement.<anonymous> (justified-image-grid.min.js?ver=4.5:1:57493)
at Function.each (jquery.min.js?ver=3.7.1:2:3129)
at ce.fn.init.each (jquery.min.js?ver=3.7.1:2:1594)
at e.fn.justifiedImageGrid (justified-image-grid.min.js?ver=4.5:1:57422)
at initJIG ((index):85:502)
window.jigAddLightbox1 @ (index):85
f @ justified-image-grid.min.js?ver=4.5:1
a.createGallery @ justified-image-grid.min.js?ver=4.5:1
a.init @ justified-image-grid.min.js?ver=4.5:1
e.justifiedImageGrid @ justified-image-grid.min.js?ver=4.5:1
(anonymous) @ justified-image-grid.min.js?ver=4.5:1
each @ jquery.min.js?ver=3.7.1:2
each @ jquery.min.js?ver=3.7.1:2
e.fn.justifiedImageGrid @ justified-image-grid.min.js?ver=4.5:1
initJIG @ (index):85
(anonymous) @ (index):86
e @ jquery.min.js?ver=3.7.1:2
t @ jquery.min.js?ver=3.7.1:2
setTimeout (async)
ce.readyException @ jquery.min.js?ver=3.7.1:2
(anonymous) @ jquery.min.js?ver=3.7.1:2
e @ jquery.min.js?ver=3.7.1:2
t @ jquery.min.js?ver=3.7.1:2
setTimeout (async)
(anonymous) @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
fire @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
t @ jquery.min.js?ver=3.7.1:2
setTimeout (async)
(anonymous) @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
fire @ jquery.min.js?ver=3.7.1:2
c @ jquery.min.js?ver=3.7.1:2
fireWith @ jquery.min.js?ver=3.7.1:2
ready @ jquery.min.js?ver=3.7.1:2
P @ jquery.min.js?ver=3.7.1:2
jquery.min.js?ver=3.7.1:2 Uncaught TypeError: $(…).JIGphotoSwipe is not a function
at window.jigAddLightbox1 ((index):92:258)
at f (justified-image-grid.min.js?ver=4.5:1:29335)
at a.createGallery (justified-image-grid.min.js?ver=4.5:1:24358)
at a.init (justified-image-grid.min.js?ver=4.5:1:17852)
at new e.justifiedImageGrid (justified-image-grid.min.js?ver=4.5:1:57366)
at HTMLDivElement.<anonymous> (justified-image-grid.min.js?ver=4.5:1:57493)
at Function.each (jquery.min.js?ver=3.7.1:2:3129)
at ce.fn.init.each (jquery.min.js?ver=3.7.1:2:1594)
at e.fn.justifiedImageGrid (justified-image-grid.min.js?ver=4.5:1:57422)
at initJIG ((index):92:502)

That appears to be a paid plugin, so generally you get free support with it. You should be contacting the plugin developer first.
sometimes elements dont display or display incorrectly if they are too close in size to the parent container. Try setting its size to something smaller and see if that works?