Variable product “add to cart” button

Hi,
I have my product table build with WooCommerce Product Table Lite.
PROBLEM:
When I click on “Add to cart” of a product with variable content I have a pop up.
This pop on the first time I click does not work properly, so I close it and if I click again on “Add to cart” and work perfectly.
The first time it shows the -+ unit number in vertical, the plus is outside the box, not visible, so the button “Add To Cart” bigger than usual, is inactive, even after I “choose an option”.
The only difference that I notice between the 2 times, that on the first time (when the pop up is not working) I have a loading message.

Does someone have a suggestion on how to solve this annoying problem? I searched online and I did not find anything.

Many thanks