Users contacts missing after failing over and then failing back pool

Question

We have 2 Lync enterprise pools that are paired.
3 days ago, I failed the central management store, and all users from pool01 to pool02.
This morning, I failed the CMS and all users back from pool02 to pool01.
All users signed back in to Lync and no issues were reported. A user then contacted me to say that his contact list was empty.
I had him sign out and back in to Lync, and also had him sign into Lync from a different workstation, as well as his mobile device. All of which showed his contacts list as empty.
We have unified contacts enabled (Hybrid mode with Office 365 exchange online, and Lync on prem). When I check the users Outlook contacts, I can see all of his contacts listed under "Lync Contacts", along with the current presence of each user.
If I perform an export-csuserdata for that user's userdata, the XML file contained within the ZIP file shows the contacts that he is missing.
I've also checked the client log on the workstation too, and can see that Lync can see the contacts as it lists them in the log. They do not appear in the Lync client though.
Environment details:
Lync 2013 - 2 enterprise pools running the latest December 2014 CU updates.
Lync 2013 clients - running on Windows 8.1. User who is experiencing the issue is running client version 15.0.4675.1000 (32 bit)
I have attempted to re-import the user data using both import-csuserdata (and restarting the front end services) and update-csuserdata. Both of these have had no effect.

Answer 1

Hi Eason,
Thanks for your reply. I've doubled checked and can confirm that only one policy exists, which enables it globally.
I believe this problem relates to issues that always seem to happen when ever our primary pool is failed over to the backup pool, and then failed back.
What I often see is that upon pool failback, things like response group announcements don't play on inbound calls (white noise is heard, followed by the call disconnecting), and agents somehow get signed out of queues (although they appear to be signed in to
the queue when checking their Response Group settings in their Lync client. I've also noticed that every time we fail back, a different user will come to me and report that either their entire contacts list is missing, or that half of their contacts are missing.
I am able to restore these from backup though.
This appears to happen regardless of if the failover to the backup pool is due to a disaster, or to simply perform pool maintenance on our primary pool.