Unfortunately, Avaya release 12.1 misses some bit details with E129 phones. Those hard phones had the worst issues. They forgot to include that information in the bulletin notes, so the little issue is: 3rd party phones do not auto register after the system reboot. Sometimes got unregistered automatically.
They give information about this issue in the doc SOLN376450, but the solution is to change all E129 phones. I will attach the solution pdf in this post. My worry is warn other people that have E129 phones, and to know if there is some solution for the issue make sure phone can receive and reply to IPO OPTION info. Because you know the E129, actually, are Grandstream in the brackground.
Direct link of solution doc in Avaya Support: https://support.avaya.com/ext/index?page=content&id=SOLN376450&viewlocale=en_US
They give information about this issue in the doc SOLN376450, but the solution is to change all E129 phones. I will attach the solution pdf in this post. My worry is warn other people that have E129 phones, and to know if there is some solution for the issue make sure phone can receive and reply to IPO OPTION info. Because you know the E129, actually, are Grandstream in the brackground.
Direct link of solution doc in Avaya Support: https://support.avaya.com/ext/index?page=content&id=SOLN376450&viewlocale=en_US