I checked your site again and I see the issue with the double modal popup in the Project Grid section.
Our theme uses Pretty Photo for lightbox popups. Which is build into the theme.
If you are using a separate plugin for that with the same trigger (the plus sign) then you’ll have them triggered twice.
What you can do is disable Pretty Photo in our theme by add two forward slashes before the line which enqueue the file in the enqueue.php file located in the /inc folder.
Go to Appearance > Editor and select the inc folder then the enqueue.php file.
Here is a screenshot of the line you need to comment out.