Hi,
The results page layout, including the pagination is affected by the them actually. There is one option that could actually conflict, and that is the number of results per page here: https://i.imgur.com/fLDN2AW.png
This should be set the same as the posts per page under the WordPress Settings -> Reading panel. Some themes might have a different internal option to override this value, or a separate option for the results page. Make sure to check those as well, they all should be set to the same value.
