I haven’t completely solved the mystery but I was able to display the h3 tag with display:block so at least the page isn’t empty and the message is clear. Thanks for your help.
This is very helpful, but the counts for active members on the Member Directory page are still incorrect. I copied the members-loop.php into a buddypress/members directory in my child theme and added the code where you described, but obviously the count for “All Members” and “Viewing x of x members” are coming from somewhere else.