ITS#4654, I've been running with this patch in place for several weeks.

CHANGES

@@ -4,6 +4,7 @@ OpenLDAP 2.3.28 Engineering
 	Fixed libldap ldap.conf max line length (ITS#4669)
 	Added ldapsearch bad filter pattern check (ITS#4647)
 	Fixed slapd-monitor locking with scope "subordinate" (ITS#4668)
+	Fixed slapd global access controls initialization (ITS#4654)
 
 OpenLDAP 2.3.27 Release
 	Fixed libldap dangling pointer issue (previous fix was broken) (ITS#4405)

servers/slapd/backend.c

@@ -248,7 +248,8 @@ int backend_startup(Backend *be)
 				return rc;
 			}
 		}
-
+		/* append global access controls */
+		acl_append( &be->be_acl, frontendDB->be_acl, -1 );
 		return backend_startup_one( be );
 	}