Hi,
The issue was caused by the results page live loader feature, which the theme uses. Some of the first results were displayed correctly, but when the theme loaded the next “batch” of results, those were not correct anymore.
To resolve both issues, I changed the number of results per page and the results limit both to 100 items. Now the theme live results loader will not trigger, but rather show all relevant results up to 100 items.
I can no longer see the pages there, and the missing result is also displayed as it should be.