TI TM4C1294XL Programming Issue
This is because of the way how driverlib  GPIOPinWrite function works.

void GPIOPinWrite(uint32_t ui32Port, uint8_t ui8Pins, uint8_t ui8Val)



ui32Port is the base address of the GPIO port.
ui8Pins is the bit-packed representation of the pin(s).
ui8Val is the value to write to the pin(s).


The ui8Val is the value that will be written to the port pins that are selected by the ui8Pins, not to the one specific pin. Thus your code will work if you rewrite it in the following way:

// Turn on the LEDs.
GPIOPinWrite(GPIO_PORTN_BASE, (GPIO_PIN_0 | GPIO_PIN_1), (GPIO_PIN_0 | GPIO_PIN_1));
// Turn off the LEDs.
GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_0 | GPIO_PIN_1, 0x00);