Net indicator is blinking. I tried the provided commands, as proposed, after getting the response 715:

AT+CSQ  :  +CSQ: 25,99 

AT+CPIN?  :  +CPIN: READY 

AT+COPS?  :  +COPS: 0,0,"o2 - de",7 

AT+CREG?  :  +CREG: 0,5 

Sending AT+CRESET  leads to restart, then it is working again, but after some time the issue is there again.

The board is supplied via the USB interface, which is connected to the laptop, Arduino is connected with another cable to the laptop.