Cisco 9971 "not registered" after Reset on CUCM 9.1

Question

Hello everyone,
we are experiencing a strange problem with 9971 phones:
We have two CUCM 9.1 clusters
Our production-cluster: Publisher, 3 Subscribers, dedicated TFTP, Unity Connection, CUPS
and our Lab environmant: Publisher, 1 Subscriber, TFTP on Publisher, Unity Connection, CUPS
In our production environment, 9971 phones work fine
In our lab environment, 9971 also work fine at first, but after some hours, sometimes days, or after a phone is resettet manually via CUCM administration the phone won't register anymore. After the phone is rebooted, the display briefly shows the correct directory number and line but they disappear immediatley and the phone is stuck with "Phone not registered" after that. The only way I can get the phone to register again after that is to completely reset all settings on the phone.
Both clusters are located within the same subnet, as well as the phones use the same voice vlan (manual tftp setting in both cases). It doesn't seem to be a network-related issue.
I have tested the same devices with both clusters, so the devices themselves seem to work properly too.
Has anyone experienced this sort of problem before? Any help would be appreciated.
Thanks
Matthias

Answer 1

Hi Mark,
best I can provide you with at the moment is this:
Status Messages on the phone:
Updating Trust List
Trust List Updated
SEPE840....cnf.xml.sgn (http)
VPN Error: VPN is not Configured
Also,  I have captured some Wireshark Traces. I took  one phone that was  registered and sent a reset request from the CUCM  Web-Interface. The  phone then rebooted and got stuck with "Phone not  registered" as I  described in my first post.
I unplugged the LAN  cable, put it  back in and captured what happened while the phone tried  to register  using a Span port at my access switch. You can find the pcap file attached to the first post.
Thanks
Matthias