I have the same issue with my boards.
I can confirm that it’s not a board issues, since I tested on 8 different ones. Sometimes, in random occasions after boot AT+CPIN? returns READY.
But on 99% of the cases I receive +CME ERROR: SIM not inserted.
returns the following:
Can you provide some assistance please? I have 20 GPS+GPRS boards from you, and I can’t get them out into production.