Cisco Softphones getting Unregistered frequently

[VitthalThutte]

We are facing this issue from last 10 days where Cisco Softphones getting Unregistered frequently. Agents able to take calls but his CIPC automatically will unregister in between. Its happening intermittent & not for all the agent on floor. Out of 100 agent 4 to 5 agent facing this issue. Its not same agent all the time. It keep changing.

CIPC version: 8.6.6

In wireshark we able to see where "The phones deregister and so agent get logged out because the phones keep losing connection to the primary cisco cucm(pbx)" There are no any changes happen at OSCC level and at central system as well.

Any suggestion how to fix this issue?

[Dennis Mink]

What is in the path between agents and cucm? Is it a wan link that goes down? For example. 

[VitthalThutte]

Its over WAN but at the same time other agent taking calls without any issue on same floor. Issue is happening for 4 to 5 agent at a time out of 100 agent on floor.