good news - your M5Core2 most likely is not defective. For me the issue is happening independently of whether M5Core2 is running from USB or battery. It always happens after a complete power loss. The reason it is not working as expected is that for some functions dealing with voltages you declared the parameter as float but then call them with big non float values. Here is what I changed in m5core2_power.cpp to make it work:

//--fm  Wire1.begin(22,23);
  Wire1.begin(21,22);

//--fm  mcu_voltage(3350);
  mcu_voltage(3.350);
  
//--fm  lcd_voltage(2800);
  lcd_voltage(2.800);
  
//--fm  ldo_voltage(2, 3300);  //Periph power voltage preset (LCD_logic, SD card)
  ldo_voltage(2, 3.300);  //Periph power voltage preset (LCD_logic, SD card)
  
//--fm  ldo_voltage(3, 2000);  //Vibrator power voltage preset
  ldo_voltage(3, 2.000);  //Vibrator power voltage preset

Thanks
Felix