I live in China and have a rooted Galaxy Note II. It is the China Mobile version (N7108), but I was able to root it, deknox it, and add google apps which are not normally part of the Chinese version. It worked fine for months. Then I got on a plane to the US and forgot to turn the phone off. It had the dreaded circle with the slash. When I entered *#06#, it gave null/null. I did not alter a thing on the flight.
I waited a day, rebooting it often in hopes that it would work. But it has not.
The only thing that fixes the problem is to flash the phone with the latest Samsung firmware. But, as soon as I follow this up with flashing Philz recovery which I had before, the IMEI is lost again. I can't figure out how flashing the recovery image is altering the EFS or IMEI. The challenge I have is that I don't know how to backup the EFS without custom recovery and root. But adding root and recovery loses the IMEI.