STM32L496 - FLASH Page Erase No Effect

Question

I have a project originally built for the STM32L432 that I am porting to the STM32L496. However, I am having an issue where the HAL_FLASHEx_Erase function provided by ST as part of the HAL works on one device but not the other. The two FLASH spaces of these micros are organized virtually identically (same 72-bit wide data read/writes). Only difference is the L496 has a second bank of FLASH. I have seen some users run into issues with this; I am NOT attempting to use Bank 2 or come anywhere close to it; my last address is at 0x801FFFF.

I can manually erase the FLASH using the STCube Programmer, which fills it with FFs. This then satisfies the requirement for the FLASH to be "erased" before writing, and I can write one block of data. But I cannot modify it again via code. As soon as I write the first time, I cannot clear the block of data that I'd just written (verified using the Memory window view in IAR).

Again, exact same piece of code works for one L-series, but not another. Anyone have any ideas?

HAL_StatusTypeDef HAL_FLASHEx_Erase(FLASH_EraseInitTypeDef *pEraseInit, uint32_t *PageError)
{
  HAL_StatusTypeDef status = HAL_ERROR;
  uint32_t page_index = 0;

  /* Process Locked */
  __HAL_LOCK(&pFlash);

  /* Check the parameters */
  assert_param(IS_FLASH_TYPEERASE(pEraseInit->TypeErase));

  /* Wait for last operation to be completed */
  status = FLASH_WaitForLastOperation((uint32_t)FLASH_TIMEOUT_VALUE);

if (status == HAL_OK)
{
  pFlash.ErrorCode = HAL_FLASH_ERROR_NONE;

  if (pEraseInit->TypeErase == FLASH_TYPEERASE_MASSERASE)
  {
    /* Mass erase to be done */
    FLASH_MassErase(pEraseInit->Banks);

    /* Wait for last operation to be completed */
    status = FLASH_WaitForLastOperation((uint32_t)FLASH_TIMEOUT_VALUE);

#if defined(STM32L471xx) || defined(STM32L475xx) || defined(STM32L476xx) || defined(STM32L485xx) || defined(STM32L486xx)
  /* If the erase operation is completed, disable the MER1 and MER2 Bits */
  CLEAR_BIT(FLASH->CR, (FLASH_CR_MER1 | FLASH_CR_MER2));
#else
  /* If the erase operation is completed, disable the MER1 Bit */
  CLEAR_BIT(FLASH->CR, (FLASH_CR_MER1));
#endif      
}
else
{
  /*Initialization of PageError variable*/
  *PageError = 0xFFFFFFFF;
  
  for(page_index = pEraseInit->Page; page_index < (pEraseInit->Page + pEraseInit->NbPages); page_index++)
  {
    FLASH_PageErase(page_index, pEraseInit->Banks);

    /* Wait for last operation to be completed */
    status = FLASH_WaitForLastOperation((uint32_t)FLASH_TIMEOUT_VALUE);

    /* If the erase operation is completed, disable the PER Bit */
    CLEAR_BIT(FLASH->CR, (FLASH_CR_PER | FLASH_CR_PNB));

    if (status != HAL_OK)
    {
      /* In case of error, stop erase procedure and return the faulty address */
      *PageError = page_index;
      break;
    }
  }
}

/* Flush the caches to be sure of the data consistency */
FLASH_FlushCaches();
}

/* Process Unlocked */
__HAL_UNLOCK(&pFlash);

return status;

}