Hi,
I was able to check on the issue. I can only think at something else on your website flushing the output buffer at a wrong moment.
That's because even the HikaShop hidden footer tag is displayed before the beginning of the page:
take.ms/bUuvj
And so it means that Hikashop finished the processing of the page and hand out the HTML to Joomla/the template.
So to identify the source of the problem, I would recommend several tests.
First, temporarily change the template to the default template of Joomla and see if you have the problem. If not, the it comes from something in the template. In that case, rename temporarily the templates/YOUR_TEMPLATE/html/com_hikashop folder via FTP and test again with your template. If it works, then the issue comes from the view overrides of HikaShop in your template (you can then try folder by folder and file by file to identify the file causing the issue).
Second, you can disable the system plugins one by one and test each time if you still have the problem. That would help you pin point the issue to a system plugin.
Third, you can try to install the previous version of HikaShop in order to downgrade HikaShop. That way, you'll be able to see if you still have the problem or not and confirm that it is something linked to the update or not. You can update again HikaShop after that by install the latest version install package.
Make a backup before these tests in case something goes wrong.