Okay, still got some conflicts here.
I know it's a bit out of the scope of your plugin, but since it's induced by it…
Try on the right hand sign to use the contact button : the overlay shows up, but the modal comes way after.
I suspect the Jquery version, since it was working flawlessly just before.
When enqueing the script, maybe i have to change the dependencies, or i don't know, use a more recent version of jquery, still compatible with your plugin ?
Using this atm :
wp_register_script('iziModal', get_template_directory_uri().'/js/iziModal.min.js', array('jquery'),”, false);
Got any idea ?