We have about 5 sangoma s400 phones that are not working at all, when I reboot, they can call internally and externally for about 30 seconds. After that it’s complete silence. In the UI of the phones it says “failed registration”. I replaced one phone with a p320 model and it seems to work. I have attempted to take a working phone, remove the extension off it, apply the extension of the phone im replacing, and then it has the same issue. When I try to go back to the original extension of the phone that was working, it now no longer will call out. What can I look at or attempt to solve this phone issue? Replacing to a pjsip style phone is not a solution, only a bandaid patch.