Hi,
I see that you have a characteristic in dropdown an another in radio.
The javascript function "hikashopUpdateVariant" handle radio and dropdown : but it looks like it does not handle both in the same time.
So when the javascript is processed, there is an error for the line
selection = selection + \'_\' + document.getElementById(\'hikashop_product_characteristic_\'+options[i]).value;
because the characteristic in radio display does not generate any ID..
I created a bug report ticket for that issue and I'll see with the rest of the HikaShop team how fix that problem.
Regarding the code, I'm not sure that it's a new bug (unless that before the different display mode wasn't managed).
For the moment, I recommend you to use one unique characteristic selection mode.
Regards,