CSS conflict?

I am currently using your premium version of Boost sales for WooCommerce and after I enabled Upsell and Cross sell, I noticed an issue. On the first add-to-cart of any product, it gives some lag before the pop-up appears. Then on subsequent to add-to-cart for the same product, the screen just becomes dark – as if a pop-up is supposed to show, but nothing appears. I was told that this might be a CSS conflict. Any credentials required are shared with Julian Vu on email.