Hi,
What I am trying to say, is that the issue is not related to the plugin, because it exists even when the plugin is disabled. Please check this screenshot: https://i.imgur.com/TmheNqL.png
The header was showing correctly at the time when I was testing it, although I don’t have a screenshot of it.
I have not changed any other options anywhere else, only that one configuration to redirect to the paginated results page on the search options. I did not change any files either, I did not use the FTP this time, it was not neccessary.
Since the problem persists when the plugin is not active, and I did not change anything else, I don’t think it is possible it is related to the search plugin.
If you recently update any other plugins/theme, or changed any options/pages related to page layouts, then it could explain it.