I logged in to my client’s admin account and saw the issue first-hand, then looked again at the filtering options. It turned out that for some reason it was set to Show Organizations rather than Show All entries; since all of the entries are for individuals, no entries were listed. As soon as I changed that popup and clicked the Filter button, the problem went away.
I noticed that the UI for choosing Filter by Letter was a bit odd. At first it showed only an individual letter, then later (after I clicked the Filter button as above) it showed all letters plus a small rectangle that I guessed (correctly) would show all letters.
I don’t know if for some reason I was seeing something unusual or different than what you intended. If in fact this is how it is set up visually, I suggest a small improvement would be to change the rectangle next to the list of letters to a button that says “show all letters” or similar. Otherwise it’s a bit hard to figure out how to turn off filtering by letter…
Thanks again for your help!