Assume that you configure a Common Area Phone device to have a Session Initiation Protocol (SIP) address that starts with a plus sign (+) in a Microsoft Lync Server 2013 environment. When you search for a user from the Lync address book on the device, the operation fails. However, the operation works if the SIP address starts with an ASCII character.
When user's SIP URI contain a plus sign or other characters, the SIP URI is enclosed in double quotation marks in the personal certificate Subject field (CN attribute). In this situation, the server fails to look up the user because of a parsing logic defect in the certificate subject name.
To fix this issue, install the August 2016 cumulative update 5.0.8308.965 for Lync Server 2013.