search does not work as expected

On my search page i enabled
– full text
– languages
– author
– publisher (rebranded as illustrator)

The search results are correct when I search for
– full text + language
– full text + author
– full text + publisher

but they are incorrect when i use multiple selections from the dropdowns
for instance:
– language + author
– language + publisher
– publisher + author
– full text + language + author

The search resulst presented only seem to take into account the full text + the first dropdown selection that is not set to “all items”

In case you don’t have an easy data set, use my site to see this behaviour:
https://www.bookabooka.com/prentenboeken-overzicht/