USB to serial loopback needs read to be called first

We are testing CP2108 USB to serial chips serial communication from User Space.

We connected the two interfaces ttyUSB0 and ttyUSB1 tx/rx connections.

First for a proof of concept we configured the baud rate using stty and then test tx/rx by running

cat /dev/ttyUSB0 in one terminal

echo "hello" > /dev/ttyUSB0 in another terminal and it works

Why is the data lost when I run first echo command and then cat within a second. Is this the default behavior.. Can we change this