All IP phones are registered with Subscriber but when i checking the extension details in CUCM.
Device > Phone >
In the Status and IP Address section is showing UNKNOWN whereas in IP phone IP address and Actice and Stadby Unified CM are showing.
what is CUCM version u are using and is this happening for any specific phone models ?
Did u try changing[upgrading] the firmware of any problematic phone model?
Thanks for replying on this case.
CUCM version is 9.1.2 and I am facing the same problem in each IP phones.
Recently I have upgraded firmware of all CP7821 IP phones in our network.
thank you for your update on the case.
I opened the TAC case for the same issue and TAC engineer had given the same solution as you suggested above.