STM32 Virtual COM port baud rate
The CDC_Transmit_FS implementation is buggy (at least in the version I am looking at):

uint8_t CDC_Transmit_FS(uint8_t* Buf, uint16_t Len)
{
  uint8_t result = USBD_OK;
  /* USER CODE BEGIN 8 */
  USBD_CDC_SetTxBuffer(hUsbDevice_0, UserTxBufferFS, Len);  
  result = USBD_CDC_TransmitPacket(hUsbDevice_0);
  /* USER CODE END 8 */
  return result;
}


As you can see the Buff parameter is never used in the function.
You might try modifying the function, by copying the Buff into UserTxBufferFS (using memcpy or whatever).