I have a Cisco SIP phone in my home office and it is normally working just fine, but from time to time it decides to unregister and then I cannot make any calls. Oddly enough the phone allows me to start the call, but then 3CX is telling me that the phone isn't registered... I have already checked the registration expiration and it is set to 600 which is just 10 minutes. So, way below the 30 minutes limit. The problem normally resolves itself within the next 30 minutes... Any ideas what could be wrong? Thank you!