Good call... I grabbed some SDL traces from CUCM and filtered these traces by mac address of my ATA. I saw that SIP messages where coming from two different IP addresses with that same MAC address. After going through the traces and looking at when the ATA issued the "IP Address Released" status message I was able to find that they were related... After changing the port to be configured for sw access vlan <voice VLAN> and removing the switchport voice vlan command, the customer is no longer complaining about the issue and I am no longer seeing the status messages "IP addr ess released" from the phone gui.
I found a fix to the issue. Ping the ATA 187 to make sure there is connectivity. Using Putty Telnet (Not SSH) to the device on port 7870. You will get a prompt as this / # Enter the command "reboot cli" After few seconds, the ATA will re-register with CUCM