Basic, fundamental feature, almost unusable, and we are a graphics shop so having to resort to workarounds is a drag on our workflow. This has only been since high sierra, I have been hunting for a solution for months but so far no joy. Searching from the finder itself (outside of adobe) works fine however. If we add a number to the search term the search breaks completely, returns nonsense results or nothing at all.
Searching using a single word works kind of, go to import an image, window opens, select image folder, type search term, search immediately switches to main graphics folder instead of images folder and begins searching there, manually click on images folder at top of window, search now switches to images folder and produces result.
Since upgrading to high sierra the search function has not worked properly at all from within adobe suite.
At our office we have 2 macs using high sierra or mojave and another offsite also using high sierra.