After an Exchange 2013 CU Update always remember to add / restore the app settings for OWA integration in the Exhange 2013 OWA “web.config” file on your Exchange 2013 Server. Typically located in the folder C:Program FilesMicrosoftExchange ServerV15ClientAccessOwa)
The CU updates to Exchange 2013 overwrites the web.config and removes your app settings for Lync integration with OWA and it breaks. An annoying one but always good to have a backup of the setting for next time around and a reminder.
Add the Certificate thumprint and Lync Server / Pool Name and recycle the OWA App Pool / issreset and your should be back in business.
Link to Technet for Lync and OWA 2013 integration for OWA