Hmm, and you have the layout set to "Default" now? Sure nothing has changed, indeed...
Well, then I'd blame it on your template. Not sure how familiar you are with the file structure of it so you could find (and possibly fix) the culprit. Another simple way to verify what your template does and what not, is you changing the Joomla template to the "classic" Protostar. If your HikaShop product page layout is set to "Default" and then the tabs are gone, the JSN template is the cause, obviously.
(Side note: The description tab is not empty, it's only white text on white background.)