As for the quick view, the AJAX requests gives 500 Internal Server error. 500 Internal Error says about some issue on the server and can be caused by different things. Anyway, to understand its nature you need to see your server error logs or enable PHP error display on the website. If you can’t do this, you need to contact your hosting provider for help in this question. Here is an article that may help you understand the error better http://www.wpbeginner.com/wp-tutorials/how-to-fix-the-internal-server-error-in-wordpress/
I see, that the plugin overrides HTML code, but it doesn’t make us feel better. There are some incompatibility with this plugin. We need to looking for solution.
About quick view:
It seems that quick view doesn’t work with products where have added extra options using this plugin.
Yes, but we are not able to change the HTML of the plugin. If you need to make the button look better with our theme then you need to ask plugins developers to add this span tag to the button. Or ask them where to change this and we will do this for you.
As for the quick view, anyway, we need to see the error first.