I could not find this documented, but I have replicated this on 22.11, 23.05 and 23.11, both on our own systems and a sampling from the Koha demo sites page. If you leave the first field blank on the advanced search screen, and complete the 2nd and 3rd fields, when you perform the search, Koha shifts up the search terms, so the operators no longer are associated with the desired term. If you click "Return to the last advanced search", that is exactly how Koha now displays it. For example: KW: <blank> AND KW: water NOT Title: waterloo Perform the search and then click "Return to the last advanced search". Koha displays: KW: water AND Title: waterloo NOT KW: <blank>
We used to have a similar problem with the selected search options. Maybe the old bug and solution can be helpful in solving this: bug 7607