Hmm, what exactly do you expect from your main loop code?
while (1) {
HAL_UART_Receive(&huart1,buf,200,500);
HAL_Delay(500);
i++;
}
From my point of view your code puts the UART into receive mode for 500ms, then sleeps for another 500ms without being able to receive data. This may work or not, it's a question of chance if you are in receive mode when you transmit your test data. By removing the delay function you just increase the chance for successful reception.
Take a look at HAL_UART_Receive_DMA() or HAL_UART_Receive_IT() functions instead to receive data in the background of your main program execution.
HTH,
Tobias
