When the form is up to "Billing info" it requires you to add a country, however it does not allow United States (or any other country for that matter)

I have been testing this and I was able to get it working on my end, please see this screen-cast: 

I got the error at the end since I'm using testing payment info. The address section is part of the payment field so, please make sure that you're filling all the fields in order to avoid the required error to be triggered. 

I have also cleared your forms cache, may you please try again and let us know if the problem persists? 

In case it still happens, please let  us know which  device were you using and try using incognito mode as well, this way you may find if it's a browser's cache issue. 

Please let us know how it goes.