Mail failing to search correctly appears to be an ongoing, sporadic issue which can be found all around the web. I had the exact problem several weeks ago requiring a complete rebuild of all Mailboxes to get it working again.
Yesterday I did an upgrade to Sonoma 14.3.1 and today my Mail search is not working (I didn’t do any Mail searches yesterday). It makes me wonder if this is coincidence as the last time I lost Search would be (roughly) when I last did a system update.
Has anyone noticed a correlation between system updates and mail search failing? Has anyone’s Mail Search failed after updating Sonoma to 14.3.1?