I use WP7609. Every 5 seconds, the microcontroller will send AT+CPIN? Command to check for sim card presence.
I found that when the signal strength is weak (around -70 to -75 db), the modem can return “Sim not inserted” within 20 to 30 minutes when idling. Take note the data SIM card is new.
After this status stays for around < 10 seconds, the modem starts to search for network.
If it possible that the status will return “sim not inserted” when the modem is initialising & prepare to search the network ?
then you need to get one to isolate if this is related to your hardware or SIM card or network.
From my experience with mangoh board, i never saw such issue that “+CPIN responded with “sim not inserted” during low signal strength”