Search by Manufacturer filter not working

Hi

I have a test site https://shop.webhandler.co

There is only on set of 5 items to test, 2 manufacturers.
https://shop.webhandler.co/index.php?main_page=index&cPath=65

if I try to sort by one or other of the manufacturers listed, nothing filters.
index.php?main_page=index&cPath=65&sort=20a&action=multiple_products_add_product is the url which doesnt look like the search is filtering.
if I use another test site, I get an ID on the search string in the url like:
index.php?main_page=index&cPath=5&sort=20a&filter_id=2

Is this a bug? or do you know of a setting I may have changed?
I am using the Hoki template on both test sites which was paid for but the support isn't very good.

Not a bug as far as core ZC goes. Probably something with the alterations made by your addons. (template)

There's a validation issue with the page which may cause some of the issue, though not entirely sure either because can't seem to sort by any of the typical sort options that could be applied at the category page.

Check this html validation.

Thank you people, I'll try adding in some other categories, but it shouldn't be a template issue per say, as the other test site that is working, shop2.webhandler.co is on the same template - it just has more of the old sample data still in there.