I2c stops working without usb

Products & Technology XIAO
#1

hi,
im using an ICM20649 from adafruit, it is unable to initialise the sensor if not started from a fresh upload - ie if i reconnect the usb or turn on the lip it will start the program but upon starting the ICM callout it fails. does anyone know why?
many thanks

#include <Adafruit_ICM20649.h>
#include <Adafruit_Sensor.h>
#include <Wire.h>

Adafruit_ICM20649 icm;
float gyroAvY;
int avNum = 10;

void setup(void) {
  pinMode(LED_BUILTIN, OUTPUT);

  if (!icm.begin_I2C()) {   //try and connect using i2c, if this doenst work, flash the LED
    for (int i = 0; i < 50; i++) {
      digitalToggle(LED_BUILTIN);
      delay(50);
    }
  }


  for (int i = 0; i < 10; i++) {      //show that start up is taking place
    digitalToggle(LED_BUILTIN);
    delay(500);
  }
  icm.setGyroRange(ICM20649_GYRO_RANGE_2000_DPS);
}

void loop() {

  //  /* Get a new normalized sensor event */
  sensors_event_t accel;
  sensors_event_t gyro;
  sensors_event_t temp;
  for (int i = 0; i < avNum; i++) {
    icm.getEvent(&accel, &gyro, &temp);
    gyroAvY += gyro.gyro.y;
  }

  gyroAvY = gyroAvY / avNum;
  if (gyroAvY > 6) {
    digitalToggle(LED_BUILTIN);
  }
  Serial.print(gyroAvY);
  Serial.println();
}