One step that often is overlooked after installing the cumulative updates for Lync or Skype for Business Server, is updating the databases.
For a Standard Edition server you need to run “Install-CsDatabase -Update –LocalDatabases”, also update your Monitoring Database with “Install-CsDatabase -ConfiguredDatabases -SqlServerFqdn <FEBE.FQDN>”.
For an Enterprise Edition server you need to run “Install-CsDatabase -Update -ConfiguredDatabases -SqlServerFqdn <SQL Server FQDN>”, and also update your Monitoring Database with “Install-CsDatabase -ConfiguredDatabases -SqlServerFqdn <FEBE.FQDN>”.
See this knowledge base article for more details and instructions for both Standard and Enterprise edition. Reading it before installing the update is worth your time!