Hi,
I was able to login.
If I add the line:
<?php exit; ?>
at the end of the show_default view file, I can see the content of the product page correctly (minus the template modules, etc of course). So this means that there is something else on your website altering the display of the page and messing up with it.
I've looked a bit at your system plugins, tried changing your template, not I couldn't find what is doing that, but at least, thanks to that debug, we know that the problem is not in HikaShop but in something else screwing up the HTML.