Blank popup window when checking the box "Use the same address as for billling"

-- url of the page with the problem -- : www.veggievore.com/dvd/checkout
-- HikaShop version -- : 3.5.1
-- Joomla version -- : 3.8.12
-- PHP version -- : 7.2.7
-- Browser(s) name and version -- : Google Chrome for Windows 10
-- Error-message(debug-mod must be tuned on) -- : There is no error message. Instead a blank popup window displays as soon as a person removes the checkmark from the box that says "Use the same address as for billing"

A blank popup window displays as soon as a person removes the checkmark from the box that says "Use the same address as for billing"

To replicate this you put something in the cart and then click on the email you have received to verify the account. You can see the blank popup window when you try to check the box that states that the address for billing is not the same.

Thank you very much. I am expecting the site to work much better now that I have changed these three things. And, thanks for pointing me to the place to turn off the legacy layouts. I like it much better now.

Sean