Need some help on this error. We are currently running CUCM 10.5 and most of our phone are using SIP and have no problems registering. We have several remote sites and they are also not having any issues. We are currently setting up a new site and the firewall that we currently use is changing from a Sophos UTM to the Sophos XG. While testing the phones, the device will register fine, then after 60-90 seconds, it will start registering again. It consistently does this through out the day. I have engaged Sophos support, and from what we can tell, there is nothing blocking UDP and the device does not drop any packets, however we cannot get it to stay registered. When looking at the phone logs, I am seeing UCM-closed-TCP consistently in the logs, which appears that something is causing this to happen. We did unload all the SIP modules on the FW, but that did not help either. When we test with an older device 7960, which uses SCCP, the device stays connected and registered. Does anyone have any suggestions on what else to look at?
