Internal server error when there are more than 3 results pages

-- url of the page with the problem -- : www.chromothesis.gr
-- HikaShop version -- : 3.2.0
-- Joomla version -- : 3.8.2
-- Error-message(debug-mod must be tuned on) -- : Internal server error

I have this problem with filters, when there are many search results and we navigate thru results pages, on page 4 (with 12 results per page) we get internal server error and the URL looks something like this huge thing:
* For example if I search for the term "αυτοκόλλητα" (you can copy-paste the term to see the results on our website)

www.chromothesis.gr/index.php/search/pro...mit=12&limitstart=24


I understand it has to do with the language being non-english, but I get the feeling that every "next page" we click the same code is added to the url again and again.

Can you please help me?

Thank you for your advice, it works