upgraded from v8 to v11 and some phones become unregistered

[t3rm3y]

We recently upgrade a customer from version 8 to 11.1 (8 - 8.1 - 11 - 11.1)
The customer has noted that if they move a phone to another desk or a phone reboots it then becomes stuck on retrieval successful but does not log the user in, or allow the user to log in.
Within system status under H.323 extensions the users base extension is under "unregistered".
If we make a small change such as a name change and merge it the unregistered user then comes alive and is logged in correctly almost instantly.
The phone is using sw version 6.6604 which i believe is the correct version for 11.1

We originally upgraded from 8-8.1-11 but as the fault occurred then we then upgraded to service pack 1 hoping it would fix it.
Customer has also had a replacement SD card and all handsets have been defaulted (Mute CRAFT #) and reprogrammed with a fresh base and password.

Has anyone else seen this or aware of a fix?

 

[t3rm3y]

the image is what the user sees when the phone is rebooted and becomes unregistered.
They are not able to log in or use it unless we make a change which then livens the phone.