Problem with Heading Calculation

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I'm using ST MotionFX v2.7.1 and have encountered an issue with heading calculation.

I'm following the sample code from the document:
um2220-getting-started-with-motionfx-sensor-fusion-library-in-xcubemems1-expansion-for-stm32cube-stmicroelectronics

#define STATE_SIZE (size_t)(2450)
static uint8_t mfxstate[STATE_SIZE];
MFX_knobs_t iKnobs;
MFX_input_t data_in_scale;

void main() {
    /* Sensor Fusion API initialization function */
    MotionFX_initialize((MFXState_t *)mfxstate);

    /* Modify knobs settings & set the knobs */
    MotionFX_getKnobs((MFXState_t *)mfxstate, &iKnobs);

    iKnobs.LMode = 2;
    iKnobs.modx = 1;
    iKnobs.output_type = 1;
    iKnobs.start_automatic_gbias_calculation = 1;
  
    //orientation

    MotionFX_setKnobs((MFXState_t *)mfxstate, &iKnobs);

    MotionFX_enable_6X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);
    MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);

    /* Enable 9-axis sensor fusion */
    MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_ENABLE);

    // init last_time
    clock_gettime(CLOCK_MONOTONIC, &last_time);

    get_sensor_data_scale(&data_in_scale);

    MFX_input_t sensor_in;
    MFX_output_t sensor_out;

    for(int i =0; i< 9999999999; i++)
    {
        get_sensor_data(&sensor_in);

        float delta_time = get_delta_time();
        MotionFX_propagate((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time);
        MotionFX_update((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time, NULL);

        printf("Heading: %f\n", sensor_out.heading);
    }
}

When I run the code, the heading value is incorrect. However, if I re-run MotionFX_initialize, the heading calculation becomes correct.

#define STATE_SIZE (size_t)(2450)
static uint8_t mfxstate[STATE_SIZE];
MFX_knobs_t iKnobs;
MFX_input_t data_in_scale;

void main() {
    for(int i =0; i< 9999999999; i++)
    {
        /* Sensor Fusion API initialization function */
        MotionFX_initialize((MFXState_t *)mfxstate);

        /* Modify knobs settings & set the knobs */
        MotionFX_getKnobs((MFXState_t *)mfxstate, &iKnobs);

        iKnobs.LMode = 2;
        iKnobs.modx = 1;
        iKnobs.output_type = 1;
        iKnobs.start_automatic_gbias_calculation = 1;

        //orientation

        MotionFX_setKnobs((MFXState_t *)mfxstate, &iKnobs);

        MotionFX_enable_6X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);
        MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);

        /* Enable 9-axis sensor fusion */
        MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_ENABLE);

        // init last_time
        clock_gettime(CLOCK_MONOTONIC, &last_time);

        get_sensor_data_scale(&data_in_scale);

        MFX_input_t sensor_in;
        MFX_output_t sensor_out;

        get_sensor_data(&sensor_in);

        float delta_time = get_delta_time();
        MotionFX_propagate((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time);
        MotionFX_update((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time, NULL);

        printf("Heading: %f\n", sensor_out.heading);
    }
}

Does anyone know why this happens? Any insights would be greatly appreciated! Let me know if you need more details.