Hi,
This issue is something coming from Joomla :
forum.joomla.org/viewtopic.php?t=952756
With a recent version of Joomla you should have the patch mentioned there.
However, some of the patch requires modifications in a view file of com_search. If you have a view override for it in your template, then it's possible that you still have the issue because of that.
So first thing to do is check if you have the folder templates/YOUR_TEMPLATE/html/com_search and if you do, try to rename it to deactivate the view overrides for the search system.
If that still doesn't help, please post on the Joomla forum as this issue is not relative to HikaShop. As a proof, if you search for the title of a Joomla article on your website you'll get the same issue:
/search?searchword=about&ordering=newest&searchphrase=all&limit=20&areas[0]=content