Why the AI answer can differ from the results below it
The answer on top and the list underneath are produced by two different processes.
The list finds every page that mentions your words and ranks them by how well they match. A page can rank highly because your words appear on it often, without that page answering anything.
The answer reads a small number of the closest pages properly, and only writes something when those pages actually state it. It is answering the question rather than matching the words. So the answer will sometimes quote a page that is not first in the list, and that is expected.
Sometimes it declines while results are showing. For staff, that is one of the most useful things the product shows. Your words appear across many pages, but none states the answer plainly. Almost always it means the answer is not written down anywhere on your site, and one short paragraph on the right page fixes it.