I have encountered many times a phenomenon that once a place the EC25-G on frequency band and it starts scanning for suitable cell it disconnects from the network.
It goes from AT+COPS=0 to AT+COPS=2. I try to change it back by entering AT+COPS=0 and get +CME ERROR: 13. It take a minute or two and then I can go back to AT+COPS=0.
My firmware version is EG25GGCR07A02M1G_126.96.36.199