We upgraded from V12 (full backup) to V15 install using backup file for configuration. We have 25 Yealink T48G phones and about half of them needed the firmware updated. Upon doing so, 8 of them would not register. Did a factory reset, deleted the phones from the extensions and tried to re-assign. 6 of them connected and are working to a certain extent but 2 of them refuse to register. Also, the phones that were on DND for the weekend when connecting to the new system are stuck in DND mode (even though it doesn't show on the phone or the softphone connected). calls to those phones don't ring and go directly to voicemail. Tech support has been looking into logs and wireshark data all day and has no suggestions. Any thoughts?