In this link: https://wordpress.org/support/topic/strange-search-error/
The user 'rundlof' wrote:
I have seen this on non-WordPress sites too, only Chrome. I believe it is an autocomplete entry created as a result of an error thrown by fbevents.js. The message appears on many sites because the search input element often has the attribute name=”s”. Clear the entry by hitting Shift + Del when it is highlighted. Hope that helps!
That solved it. Hit Shift+Del when it's highlighted.