The solution should be to run Update-CsAddressBook but this will not solve your problem.
After reading the Lync Server 2013 release notes it is clear that you should run the cmdlet Debug-csAddressBookReplication.
If the cmdlet reports that there are no unindexed or abandoned objects, the error event 20154 can be safely ignored.
Running the Debug-csAddressbookRelication cmdlet shows that are 4 objects not indexed that should be.
This Lync Server 2013 deployment is running in a Exchange Server 2010 environment so we need to set the use of the Unified Contacts Store in the Global User Service policy to false this enabled by default.
Again run the cmdlet Update-Cs|Addressbook
And now check again with Debug-csAddressbookRelication cmdlet
Now there are no Objects not indexed that should be or any Abandoned objects we could safly ignore the error event 20154.