Hi,
Please understand that this blank page happens as soon as you try to access the search page of Joomla, even if you don't search anything. So it probably isn't linked to HikaShop but something else on your website.
If there is no error message, even though you set the "error reporting" to "maximum" in the Joomla configuration then I don't see what you can do. Without errors, it's not possible to see where the problem is coming from.
So do a backup of the website with akeeab backup or similar and restore it on a local web server (wamp,xamp) on your own computer and see what error you get on that page. Hopefully, you should get an error message on your local computer.