I'm attempting to cause an STM32WL (currently on a WL55JC1 devboard) to sleep using the shutdown mode, and am running into a an issue where the MCU immediately exits sleep after it enters it.

Here's what I'm using to get into sleep:

                    Radio.Sleep();
                    HAL_SUBGHZ_MspDeInit(&hsubghz);
                    LL_RCC_RF_EnableReset();
                    __disable_irq();
                    HAL_SuspendTick();
                    HAL_PWREx_DisableSRAMRetention();
                    HAL_PWREx_EnableFlashPowerDown(PWR_FLASHPD_LPSLEEP);
                    HAL_PWR_DisablePVD();
                    HAL_SUBGHZ_ExecSetCmd(&hsubghz, RADIO_SET_SLEEP, 0x0000, 2);
                    HAL_Delay(3000);

                    HAL_PWREx_EnterSHUTDOWNMode();

When going into sleep, I attempt to suspend the systick, and then use the HAL macro to enter the shutdown sleep mode. From what I've read this seems to be all I need, but obviously not in this case.

The exit from sleep happens regardless of the onboard ST-Link module on my devboard being powered or not.

NRST is currently floating, since when I pull it to ground the chip shuts down and pulls 700uA. Another puzzle to figure out.

Edit: Not sure if it will help, but here's my system clock config:

void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure LSE Drive Capability
  */
  HAL_PWR_EnableBkUpAccess();
  __HAL_RCC_LSEDRIVE_CONFIG(RCC_LSEDRIVE_LOW);
  /** Configure the main internal regulator output voltage
  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
  /** Initializes the CPU, AHB and APB busses clocks
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSE|RCC_OSCILLATORTYPE_MSI;
  RCC_OscInitStruct.LSEState = RCC_LSE_ON;
  RCC_OscInitStruct.MSIState = RCC_MSI_ON;
  RCC_OscInitStruct.MSICalibrationValue = RCC_MSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_11;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
  /** Configure the SYSCLKSource, HCLK, PCLK1 and PCLK2 clocks dividers
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK3|RCC_CLOCKTYPE_HCLK
                              |RCC_CLOCKTYPE_SYSCLK|RCC_CLOCKTYPE_PCLK1
                              |RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_MSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.AHBCLK3Divider = RCC_SYSCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  {
    Error_Handler();
  }
}