[T48] - NTP time update fails

[DennisT]

I have over a dozen T48G phones connected to a 3CX 12 system. Most of the phones are at Firmware v35.80.0.60. One is at v35.80.0.130. All phones are working fine, except one.

IDK if this problem was from day 1 or recent (users can be inconsistent on reporting issues).

Problem: This one phone displays the wrong date/time. When rebooting it starts at 12AM on May 7. NTP updates to the NTP server show update failed in the phone system debug log (logging @ 6). Everything else on the phone appears to be working fine (making calls, receiving, vmail, etc)

The NTP server (Win 2012 R2) is set to log the ntp activity. The NTP requests/response aren't materially different than activity for a phone that does update. The server is set to update regardless of the offset.

The phone is provisioned from the 3CX server and the configuration is the same used for all T48G phones. Phone is powered via POE.

Things I've tried:
1. Reboot phone. No change.
2. Reprovision phone - No change
3. Change the phone to manual clock, set it. - Time is correct
4. Set phone back to NTP. Reboot. Time is now starting at 12AM on July 17 (today). NTP in the log still shows fail.
5. Reset phone back to factory default settings. Rejoin the 3CX server and reprovision. No change.
6. Update firmware to 35.80.0.130. Reboot. No change

I'm hesitant to upgrade the firmware further as I don't know if a newer version will still work properly with the version of 3CX I'm running.

Suggestions? Is the phone defective?