Touchscreen starts to send command 01 02 03
Uart0Receive() react on incoming data and add to queue
The code starts to process data in queue
the queue has been filled with 01 02 and now the code reads the queue again and now its empty and gives -1 and because the result is -1 then the loop ends and this time i did not receive the 03

Do you agree on this?

Yes that is correct. The event will fire again though.

And it seems that you have tested this with success so I will have to try again with little more advanced code.

Yes but not on exactly the same software and hardware version so it still can be something else.