Spotlight not finding all files

Since upgrading to Big Sur 11.4 I've noticed that Spotlight doesn't find everything it used to. It always found text in DEVONthink files, now, it finds only some.

To test this, I created a few different files in DEVONthink 3 (v. 3.7.2) with a made-up word in each. One is a Plain Text File, one is a Rich Text file, one is a Formatted file (html). Spotlight was able to find the made-up word in only the html file, but not the Plain Text or Rich Text.

Using DEVONthink's search function found all three files.

Similarly, if I open Finder and enter the made-up word in Finder's search field, it will find all three files. In addition, searching by Alfred and by Houdah also turned up all three files. Only Spotlight, when invoked by Cmd-Spacebar, failed to find all three.

I have rebuilt the Spotlight database (several times), and rebuilt the DevonThink database. The problem persists. Is anyone else having intermittent failures from Spotlight?