Hi,
Thank you for all the details, it helps a lot!
Okay, the issue here is the results grouping. The “Reflect Leven” would be very likely returned first, but there is a taxonomy grouping enabled. The taxonomy “Binnenkort” alphabetically is above the “Boeken”, as you already suggested.
There was a similar issue about a month ago. I am plannig to add an option to the grouping panel, that allows automatically re-ordering the groups by the most relevant items per each group. It should be available within the next upcoming release.