Malfunction after Host change

Hey all,
My client changed host recently and ofc his site is not working well, snap.
This is the thing, site works fine on production domain and hosting, while it’s not behaving the way it should on the new host.
Anyone can point on how to fix this matter ?

http://www.gree.hr/test/?product=vanjska-gree-u-match-jedinica-3-5-kw – NEW HOST NOT WORKING ( if you refresh the page product might show up ).

http://www.ibci.hr/test/?product=vanjska-gree-u-match-jedinica-3-5-kw – OLD HOST, everything is fine here

Thanks in Advance