UART data loss

Respected all,
This is my first query over this forum so I thank you for your support well in advance.

I am simply trying to use the following "USART_PutChar" function which would send the data bytes via uart4.

Now, my code is calling this "putchar" function each time one of my sensor receives the data.

The function is as follows:

void USART_PutChar(char *ch)
 {

        while((*ch!='\0'))
         {

                        while(!(UART4->SR & USART_SR_TXE));
                                UART4->DR = *ch;
        ch++;

   }

 }

The issue is as follows:
When the data is sent to the sensor on a slower pace, let say twice a second or so, the data is coming fine.
But when this rate increases, there is data loss and the data stops coming.

When I removed this line from the code above,

                        while(!(UART4->SR & USART_SR_TXE));

,

the data starts coming but then the data turns out bit random (full of spaces and all).

Well, this shows that the TX/RX pin is somehow causing the difference.

Can anyone kindly assist me in this regard.

Thanks
Regards