Does slapd-meta built from 2.4.31 source support using slapd-config?
You never mentioned slapd-meta in your original post. olcDbURI is usually associated with slapd-ldap. I don't believe slapd-meta has cn=config support at this time.
--Quanah -- Quanah Gibson-Mount Sr. Member of Technical Staff Zimbra, Inc A Division of VMware, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration