To solve this issue perform the following steps:

1. Go to ADMIN >> Pages
2. Look for a (hidden) page called "Search Results". if it is not present create it (in root level or child of Home) and set not to display in menu.
3. Open Search Results page and validate, that it contains a single instance of Search Results module. if not, add it.
4. If it is there delete it, and add it again to the same page.