Lync dropping calls after 1-2 seconds!

Problem Description:-

Dealing with a single user problem which is complaining that when someone call him to Lync, the call popup appear for 1-2 second and disappear.

Workaround:-

Disabling Enterprise voice feature solved the problem but left user to do not make call outside which was another problem/Limitation.

Troubleshooting:-

We started looking the UCCP and CDR logs from monitoring server for user SIP URI and understand that call is getting transfer to UM and failing as we do not have UM integration.

I also tested “Test-CSPSTN” call to user SIP and see the different error message which was pulling us to check routing problem. Most of the call were test by lync-lync  call which does not use gateway so Below error was surprises.

Solution:-

We started to think the use CSData corruption which may causing the problem. I follow below steps

## Backup specific user data
a) Export-CsUserData -PoolFqdn “POOL-FQDN” -UserFilter “test@Domain.com” -FileName “C:\temp\Testuserdata.zip ”
## this command will remove all Lync attributes from the AD accounts, it’s identical to the “Remove from lync server” in control panel.
b) Remove-CsUser –Identity Test@Domain.com
c) Re-create user in Lync, manually assign polices, enterprise voice extension etc..
## this command will restore Lync user data (contact list, logs etc..) it will append the user data instead of overrating data like in the “Import-CsUserData” cmdlet.
d) Update-CsUserData -Filename “C:\temp\Testuserdata.zip” -UserFilter test@Domain.com

Problem Solved ?? , UHH, Guess ??.  NO NO L, We have still same issue !!!!!

Again tried to above steps but did not use “Update-CsUserData” as I thought there could be some stale/bad entry in the contacts, Conference, LIS data which may be causing the issue.
Now, The problem is solved.