Mac Mail cannot find emails within certain dates
So, I've always used Mac Mails Search feature to great effect when working to find an email from a particular person, from someone with 'xyz' in their email or on a specific subject.
Issue is now when I search, no matter what I search for it doesn't display any results that were sent or received between 26th January and 26th February (inclusive) 2019.
It's driving me mad. Any pointers or advice appreciated.
Chris.
MacBook Pro 15", macOS 10.14