fds_record_write stops prematurely.

Question

Hello. 
 It is under development using nrf52832 (S132 v7.0.1, SDK v17.0.0) as a peripheral device. 
 I'm currently considering Flash Data Storage (FDS). 
 As settings, "FDS_VIRTUAL_PAGES" is set to 4, "FDS_VIRTUAL_PAGE_SIZE" is set to 1024, and the writable area is 12kB. In order to check how many times 64Byte can be written to 12kB, I created a process that repeats fds_record_write and made it work, but it is not an error and the operation stops halfway. I checked the number of times I wrote when I stopped, but the number of times was different each time. 
 #include "app_error.h"
#include "fds.h"

/* Definition of sdk_config.h */
#define FDS_ENABLED 1
#define FDS_VIRTUAL_PAGES 4
#define FDS_VIRTUAL_PAGE_SIZE 1024
#define FDS_VIRTUAL_PAGES_RESERVED 0
#define FDS_BACKEND 2
#define FDS_OP_QUEUE_SIZE 4
#define FDS_CRC_CHECK_ON_READ 0
#define FDS_CRC_CHECK_ON_WRITE 0
#define FDS_MAX_USERS 4

#define FILE_ID 0x1000 /* The ID of the file to write the records into. */
#define RECORD_KEY 0x1100 /* A key for the first record. */

typedef struct {
 uint8_t test_data_a;
 uint8_t test_data_b[6];
 uint8_t test_data_c[16];
 uint8_t test_data_d[16];
 uint8_t test_data_e[16];
 uint8_t test_data_f[8];
 uint8_t test_data_g;
} T_FDS_LOG_DATA;

static T_FDS_LOG_DATA v_fds_log_data_write;

static fds_record_t m_record =
{
 .file_id = FILE_ID,
 .key = RECORD_KEY,
 .data.p_data = &v_fds_log_data_write,
 /* The length of a record is always expressed in 4-byte units (words). */
 .data.length_words = (sizeof(v_fds_log_data_write) / sizeof(uint32_t)),
};

static fds_record_desc_t record_desc;
static uint32_t cb_write_cnt = 0;

static void fds_evt_handler(fds_evt_t const * p_fds_evt);

/* FDS related initialization function */
void fds_evt_init(void)
{
 ret_code_t err_code;

 memset(&v_fds_log_data_write, 0xAA, sizeof(v_fds_log_data_write));

 err_code = fds_register(fds_evt_handler);
 APP_ERROR_CHECK(err_code);

 err_code = fds_init();
 APP_ERROR_CHECK(err_code); 

 return;
}

/* FDS event handler */
static void fds_evt_handler(fds_evt_t const * p_fds_evt)
{
 switch (p_fds_evt->id)
 {
 // Initialization completion event.
 case FDS_EVT_INIT:
 if (p_fds_evt->result != NRF_SUCCESS) {
 // Initialization failed.
 }
 else {
 fds_data_write();
 }
 break;

 // Write complete event.
 case FDS_EVT_WRITE:
 cb_write_cnt++;
 m_record.key = (uint16_t)cb_write_cnt;
 v_fds_log_data_write.test_data_a = (uint8_t)cb_write_cnt;
 fds_data_write();
 break;

 default:
 break;
 }

 return;
}

/* FDS write process*/
void fds_data_write(void)
{
 ret_code_t err_code;

 // Write a record to Flash.
 err_code = fds_record_write(&record_desc, &m_record);
 APP_ERROR_CHECK(err_code);

 return;
} 
 Why does it stop working? Is there a countermeasure? 
 Best regards.