I've been running an authentication server in my home network for half a year
now, without problems. After a zypper dup on 2016-02-02, clients could no
longer authenticate their users (both other computers on the net and the server
itself).

Below I've quoted slapd-related error messages from the system journal during
the update.

Stopped slapd and re-ran the Yast2 Authentication server module, opted for
clean re-install (without reading current configuration). Selected starting of
LDAP and Kerberos. Default hdb backend. On clicking "Finish", there is an error
message 

    56b1f578 <= str2entry: str2ad(olcDbCheckpoint): attribute type undefined
    slapadd: could not parse entry (line=920)

Searched for a schema file containing the database-specific attributes (a web
search hinted at a confighdb.ldif file, which appears not to be present on my
system.

I'd be happy to run tests or provide further data, and of course I would also
welcome a workaround.

*.*

Feb 02 18:47:22 spunk slapd[2408]: slapd shutdown: waiting for 0
operations/tasks to finish
Feb 02 18:47:23 spunk slapd[2408]: DIGEST-MD5 common mech free
Feb 02 18:47:23 spunk slapd[2408]: slapd stopped.
Feb 02 18:47:23 spunk systemd[1]: Stopped OpenLDAP Server Daemon.
Feb 02 18:47:23 spunk audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295
ses=4294967295 msg='unit=slapd comm="systemd" exe="/
Feb 02 18:47:23 spunk audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295
ses=4294967295 msg='unit=slapd comm="systemd" exe="/u
Feb 02 18:47:23 spunk systemd[1]: Starting OpenLDAP Server Daemon...
Feb 02 18:47:23 spunk slapd[7266]: @(#) $OpenLDAP: slapd 2.4.43 $
                                           opensuse-buildservice@opensuse.org
Feb 02 18:47:23 spunk slapd[7266]: UNKNOWN attributeDescription
"OLCDBCACHESIZE" inserted.
Feb 02 18:47:23 spunk slapd[7266]: UNKNOWN attributeDescription
"OLCDBCHECKPOINT" inserted.
Feb 02 18:47:23 spunk slapd[7266]: UNKNOWN attributeDescription "OLCDBCONFIG"
inserted.
Feb 02 18:47:23 spunk slapd[7266]: UNKNOWN attributeDescription
"OLCDBIDLCACHESIZE" inserted.
Feb 02 18:47:23 spunk slapd[7266]: UNKNOWN attributeDescription "OLCDBINDEX"
inserted.
Feb 02 18:47:23 spunk slapd[7266]: config error processing
olcDatabase={1}hdb,cn=config:
Feb 02 18:47:23 spunk slapd[7266]: DIGEST-MD5 common mech free
Feb 02 18:47:23 spunk slapd[7266]: slapd stopped.
Feb 02 18:47:23 spunk slapd[7266]: connections_destroy: nothing to destroy.
Feb 02 18:47:23 spunk systemd[1]: slapd.service: Control process exited,
code=exited status=1
Feb 02 18:47:23 spunk systemd[1]: Failed to start OpenLDAP Server Daemon.
Feb 02 18:47:23 spunk audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295
ses=4294967295 msg='unit=slapd comm="systemd" exe="/
Feb 02 18:47:23 spunk systemd[1]: slapd.service: Unit entered failed state.
Feb 02 18:47:23 spunk systemd[1]: slapd.service: Failed with result
'exit-code'.
Feb 02 18:47:23 spunk start[7266]: Starting ldap-server
Feb 02 18:47:23 spunk [RPM][7214]: erase openldap2-2.4.42-18.1.x86_64: success
Feb 02 18:47:23 spunk [RPM][7214]: Transaction ID 56b0eba8 finished: 0
Feb 02 18:47:23 spunk [RPM][7290]: Transaction ID 56b0ebab started