What could be the root cause for the following log message? Extension 1010 is unregistered, removed contact: sip:email@example.com:33357;rinstance=0-jjj62bkgnkqrohnatas9jhowprzx7pyv;ob;inst="b14f8209" The 3CX system sits on the same subnet and this randomly happens with SIP phones from different vendors (Cisco, Yealink, Gigaset). It seems to normally happen right after making (or receiving) a call on the extension. Is the error indicating that phone has failed to do a renewal? Oddly enough, the extension continues to show with a green status. Is it possible that the 3CX system is expecting a register renewal after completing a call and for some reason some phones are handling this differently? That said, all phones worked fine with other SIP based PBX systems. This is a serious problem for us that needs to be resolved. As such, I really need to know if this is an issue with the phones or if it is a bug in the 3CX software. Any suggestions?