Can't export vCards from iCloud Contacts

I'm suddenly unable to export vCard from iCloud Contacts. (I only say "suddenly" because I have successfully done this numerous times before ... but I haven't tried in a real long time.)

In the "Show Actions" menu [gear icon], I click on the "Export vCard ... " command, but nothing happens. I get no dialog box (which I EXPECT to get, as indicated by the ellipses), and the vCard does not appear to export to my Mac (whether to my Downloads or Desktop folders, or anywhere else).

Tried the other two "ellipses" commands — "Preferences ... " and "Import vCard ... " and they work fine.

Thanks for any help you can offer!