Graph is not displaying correctly

Receiving data by UART and display it by TOUCHGFX cause some lost data in my screen, graph is not displayed correctly.

There are 2 boards one which is been receiving the signals by sensors and the second one is LCD board which has been configured by TOUCHGFX.

I want to receive data by UART from the first board and show them in LCD.

But some graph is not shown correctly.

Here is the code:

```

HAL_UART_Receive_IT(&huart1,(uint8_t*)RxBuf,20);

HAL_UART_RxCpltCallback(&huart1);

   HAL_Delay(1);

```

I put ```HAL_Delay(1); ``` in order to receive data correctly but it does not make sense.

And the data shown by graph:

```

   if(i<123){

dynamicGraph1.addDataPoint(RxBuf[1]+25);

}else

i=0;

```

Note : in image, the first graph is displaying by UART and as you see suddenly a drop appears... and I don't know how to solve it, and the second graph (from above) is the correct signal.

How can I solve it?

Thanks again.