This is likely to be because no relevant items are returned; if there are no results at all, it'll switch to fallback searches.
Basic question but do you use Mail.app for your email? If you navigate to ~/Library/Mail/, what does it contain? The file filters need to be pointing to the right place, so if you have no emails stored there, you'll get the behaviour you're seeing.
Thank you for the guide. I am also having a same issue.
I found my ~/Library/Mail/ doesn't contain any files in it, however if I am using Mail.app, how can I move the actual email files to this library/mail/ folder?
Mail.app search by author, subject or content [For macOS Mojave & earlier]
in Share your Workflows
Posted · Edited by sumin
Thank you for the guide. I am also having a same issue.
I found my ~/Library/Mail/ doesn't contain any files in it, however if I am using Mail.app, how can I move the actual email files to this library/mail/ folder?
BR,
Sumin