I was searching through gpa to hunt down a possible bug and I saw that the configure script looks for 'gpg2keys_ldap gpgkeys_ldap', when my gnupg package provides dirmngr_ldap. Debian 9 also has dirmngr_ldap. I don't knowingly have a way to test if it should be one or the other, but I got the impression that the key lookup has been delegated to dirmngr and the name of the binary changed.