I'm experiencing the same issue. Flashed a new Temasek CM11 nightly and after booting into the rom for the first time no PIN unlock dialogue appeared. The phone is stuck at "searching for service". My IMEI number is still there and both SIM cards I have tried work perfectly in my iPhone.
I'm still on JB 4.3 bootloader with CMW recovery 184.108.40.206 and baseband is N9005XXUBMI6. Is it possible something got messed up when flashing latest CM? Perhaps baseband/modem firmware outdated?
I'm downloading N9905XXUEND3 and will flash back completely to stock. Will report back here later.