We're celebrating Europe this week and we'd like to support all of our European Union customers by covering the VAT rate. Discount is valid for all new purchases and manual renewals and applies automatically during checkout.
While that’s not a plugin that we created or bundle with the theme, the described issues sounds like there’s a JavaScript or backend failure on your site.
With an URL, I could investigate this further. Otherwise you’ll need to use the browser’s developer console and server logs to look for any error messages.