Hi,
I tried to look at that page but I didn't see any ReCaptcha field on the registration page of HikaShop so I can't say much.
Actually no one reported such issue with our Recpatcha plugin.
Are you sure that you're using the Recpatcha plugin that we provide on our website and not another one like the one that is installed by default in Joomla ?
It could also come from your template, so if you could try to switch temporarily your template and see if you still have the issue in order to confirm that theory.