There is error here (only in Chrome)

Did you try it on default theme? Or have you customized it?

Hi. I am using my own child theme but I tried it with twentysixteen as well and it does the same. I also noticed that it does it only when I click enter when I’m trying to search. If I click outside the search input after typing it works properly. So pressing enter seems to cause the issue.

Url please.

https://demosivusto.net/royal/kohteet/ here you go.

Seem like the chrome fired multiple time when you press enter.
For easy fix, use a search button instead. Don’t use buttonless search form,as it will catch input field changes as well as press enter. This make it submit the form multiple time.

That worked. Thanks for help mate.