Default No Network After Phone Reboots

My phone is a Motorola XT1032 and when I reboot it instead of going through the routine of SIM lock PIN then phone lock PIN, it just goes straight to the phone lock with no network connection.

This firstly occurred at work yesterday when distractedly I ended up in "Safe mode", which doesn't work for me in any case as there's a bug or whatever somewhere which is by the by. So after rebooting a warning triangle and exclamation mark was showing in the status bar where it said...."Your selected network (3) is not available", 3 being my network in the UK. I then did the obvious: removed the SIM, gave it a wipe, remounted it and hey...network back!

I was a little concerned that perhaps the pins in the SIM card housing may be faulty so to check I rebooted my phone later on with exactly the same result and the same solution by remounting the SIM. Totally bizarre, so anyone have any ideas?

Thanks in advance,

Malc