I have 2 EX90s (TC7.1.1) on a different company network that register via H.323 and SIP to a VCS (X8.1.1). Occasionally these two will Fail registering SIP and the only way to correct it is to restart the EX90. I've tried to turn SIP Mode off and then on again. A C20 on same network has no issues, neither do any other local devices registered to the same VCS. All Configurations are identical.