MacOS Mail - Search does not work with certain phrases

entering particular words in the MacOS search box just causes it to search indefinitely.

What is going on?

I type a word, hit enter, then it just shows "searching..." for hours

Cancel it and type a different word, no problems.

Why on earth would certain words cause this?

The word in particular is "Roman"

I have had this with other phrases but until now didn't keep a record of which phrases cause the issue.