SAADC 2 Channels Reading is not working well

Question

Hi, 
 I'm trying to do a 2 channels adc reading to read a value of a potentiometer and a value of a battery level. When I try to make it, I saw that sometimes, the value of the battery level gets into the buffer[0] where I only want values of the potentiometer. Here's my code : 
 #define SAMPLES_IN_BUFFER 1 
static nrf_saadc_value_t m_buffer[2][SAMPLES_IN_BUFFER];

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
 if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
 {
 ret_code_t err_code;
 uint16_t MAX_VALUE = 940;

 err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
 APP_ERROR_CHECK(err_code);
 
 NRF_LOG_INFO("CHANNEL 1 %d", p_event->data.done.p_buffer[1]);
 nrf_delay_ms(50);

 if (p_event->data.done.p_buffer[0] <= get_threshold()){
 speed = 0;
 if (m_count_connected > 0) {
 led_green();
 }
 } else{
 speed = floor(p_event->data.done.p_buffer[0] * (get_sensitivity() / 4.0));
 if (m_count_connected > 0) {
 led_turquoise();
 }
 }

 if (speed > MAX_VALUE){
 speed = MAX_VALUE;
 }
 
 speed_8bits = speed / 3.68;
 pourcent_speed = floor(speed*100/MAX_VALUE); 
 //NRF_LOG_INFO("SPEED %d, SPEED_8BITS %d, PERCENT %d", speed, speed_8bits, pourcent_speed);

 //if (abs(potentiometer_last_value - speed_8bits) > 1) {
 // idle_time_reset();
 // restore_last_color();
 // potentiometer_last_value = speed_8bits;
 // potentiometer_value_handler(potentiometer_last_value);
 //}

 //if (is_wired_mode()) {
 // motor_oscillate();
 //}
 }
}

void saadc_init(void)
{
 ret_code_t err_code;
 nrf_saadc_channel_config_t channel_0_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN5);
 nrf_saadc_channel_config_t channel_1_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN4);

 err_code = nrf_drv_saadc_init(NULL, saadc_callback);
 APP_ERROR_CHECK(err_code);

 err_code = nrf_drv_saadc_channel_init(0, &channel_0_config);
 APP_ERROR_CHECK(err_code);
 err_code = nrf_drv_saadc_channel_init(1, &channel_1_config);
 APP_ERROR_CHECK(err_code);

 err_code = nrf_drv_saadc_buffer_convert(m_buffer[0], SAMPLES_IN_BUFFER);
 APP_ERROR_CHECK(err_code);
 err_code = nrf_drv_saadc_buffer_convert(m_buffer[1], SAMPLES_IN_BUFFER);
 APP_ERROR_CHECK(err_code);
} 
 What am I doing wrong ? 
 Thanks, 
 Chris