Why does the GPIOTE event not link to the GPIOTE task via PPI though the event handler works?

Question

I was learning GPIOTE using the example provided in SDK 9.0.0. (examples\peripheral\gpiote). The example only uses GPIOTE task and a timer to drive the task through PPI.

So I created a similar function (pasted below) that is meant to link a GPIOTE event to a GPIOTE task through PPI. The GPIOTE event corresponds to button 2 (BSP_Button_1) of the nRF51 DK board. The GPIOTE task corresponds to LED 2 (BSP_LED_1).

The GPIOTE event's handler also toggles LED 3 (for verification purposes).

LED 3 toggled when button 2 was pressed, confirming that the GPIOTE event was working. But LED 2 was always on. So either PPI or GPIOTE task, or both was not working.

#include <stdbool.h>
#include <stdint.h>
#include "nrf.h"
#include "nrf_gpiote.h"
#include "nrf_gpio.h"
#include "boards.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "nrf_drv_gpiote.h"
#include "app_error.h"
#include "nrf_delay.h"

#ifdef BSP_LED_0
    #define GPIO_OUTPUT_PIN_NUMBER BSP_LED_0  /**< Pin number for output. */
#endif

#ifndef GPIO_OUTPUT_PIN_NUMBER
    #error "Please indicate output pin"
#endif


static nrf_drv_timer_t timer = NRF_DRV_TIMER_INSTANCE(0);

void timer_dummy_handler(nrf_timer_event_t event_type, void * p_context){}

	
#define GPIO_LED_PIN 			BSP_LED_1
#define GPIO_LED2_PIN			BSP_LED_2
#define GPIO_BUTTON_PIN   BSP_BUTTON_1

void button_handler(nrf_drv_gpiote_pin_t pin, nrf_gpiote_polarity_t action) 
{
	nrf_gpio_pin_toggle(GPIO_LED2_PIN);
	nrf_delay_ms(1000);
}
	
static void led_button_setup()
{
  uint32_t gpiote_event_addr;
  uint32_t gpiote_task_addr;
  nrf_ppi_channel_t ppi_channel;
  ret_code_t err_code;
	
	// Initialise the LED task GPIOTE
  nrf_drv_gpiote_out_config_t task_config = GPIOTE_CONFIG_OUT_TASK_TOGGLE(false);

  err_code = nrf_drv_gpiote_out_init(GPIO_LED_PIN, &task_config);
  APP_ERROR_CHECK(err_code);

  gpiote_task_addr = nrf_drv_gpiote_out_task_addr_get(GPIO_LED_PIN);

  nrf_drv_gpiote_out_task_enable(GPIO_LED_PIN);

	// Initialise LED 2 as an output
	nrf_gpio_cfg_output(GPIO_LED2_PIN);
	
	// Initialise the button event GPIOTE
  nrf_drv_gpiote_in_config_t event_config = GPIOTE_CONFIG_IN_SENSE_HITOLO(false);

  err_code = nrf_drv_gpiote_in_init(GPIO_BUTTON_PIN, &event_config, button_handler);
  APP_ERROR_CHECK(err_code);

  gpiote_event_addr = nrf_drv_gpiote_in_event_addr_get(GPIO_BUTTON_PIN);
	
  nrf_drv_gpiote_in_event_enable(GPIO_BUTTON_PIN, true);

  // Initialise the ppi channel
  err_code = nrf_drv_ppi_channel_alloc(&ppi_channel);
  APP_ERROR_CHECK(err_code);

  err_code = nrf_drv_ppi_channel_assign(ppi_channel, gpiote_event_addr, gpiote_task_addr);
  APP_ERROR_CHECK(err_code);

  err_code = nrf_drv_ppi_channel_enable(ppi_channel);
  APP_ERROR_CHECK(err_code);

	
}

static void led_blinking_setup()
{
    uint32_t compare_evt_addr;
    uint32_t gpiote_task_addr;
    nrf_ppi_channel_t ppi_channel;
    ret_code_t err_code;
    nrf_drv_gpiote_out_config_t config = GPIOTE_CONFIG_OUT_TASK_TOGGLE(false);

    err_code = nrf_drv_gpiote_out_init(GPIO_OUTPUT_PIN_NUMBER, &config);
    APP_ERROR_CHECK(err_code);


    nrf_drv_timer_extended_compare(&timer, (nrf_timer_cc_channel_t)0, 200*1000UL, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);

    err_code = nrf_drv_ppi_channel_alloc(&ppi_channel);
    APP_ERROR_CHECK(err_code);

    compare_evt_addr = nrf_drv_timer_event_address_get(&timer, NRF_TIMER_EVENT_COMPARE0);
    gpiote_task_addr = nrf_drv_gpiote_out_task_addr_get(GPIO_OUTPUT_PIN_NUMBER);

    err_code = nrf_drv_ppi_channel_assign(ppi_channel, compare_evt_addr, gpiote_task_addr);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_enable(ppi_channel);
    APP_ERROR_CHECK(err_code);

    nrf_drv_gpiote_out_task_enable(GPIO_OUTPUT_PIN_NUMBER);
}

/**
 * @brief Function for application main entry.
 */
int main(void)
{
    ret_code_t err_code;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_gpiote_init();
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_timer_init(&timer, NULL, timer_dummy_handler);
    APP_ERROR_CHECK(err_code);
    *(uint32_t *)0x40008C0C = 1;

    // Setup PPI channel with event from TIMER compare and task GPIOTE pin toggle.
//    led_blinking_setup();

	  led_button_setup();
	
    // Enable timer
//    nrf_drv_timer_enable(&timer);

    while (true)
    {
        // Do Nothing - GPIO can be toggled without software intervention.
    }
}