I'm using a GSM Module with Arduino along with Node MCU. I have a supply of 9V, 2A in the DC jack of the Arduino and the GSM Shield. The Node MCU is powered from the 3.3V of the Arduino. I can receive messages fine in the GSM when the USB port of the Arduino (including the power supply I mentioned earlier) is connected to the laptop through and monitored using the serial monitor. However if I remove the USB port, the GSM cannot receive the messages anymore but when I press the reset button of the Arduino, it will start receiving messages again. Why does it only works when I reset the Arduino first after powering it up?