Search bar in header not working

When using the search bar in the header it always shows "no results found" regardless of query.
In the Log it says [ AttributeError: 'SearchHandler' object has no attribute 'default_sort_on' ]

The search block works fine.
Searching in the backend works fine and the API appears to give proper responses as well.
I created a new page and used the same frontend. There, the search bar works fine.
An interersting behaviour is that the search reults page had a tag, which got removed after I removed it from all other pages.

Any ideas what could be the cause?

I managed to fix it by setting the default sorting in the control panel to 'relevance'. Before that it was 'alphabetically'.
Changing it back to anything but relevance doesn't break the search function. Instead it only breaks the result set under 'sort by relevance'. That means you can always change the sorting order of the reult set to something different.
If, however, the initial search has no results, the search function breaks again until the default sorting in the control panel is set to 'relevance' again.