Riva 9600 baud rate is 1200Bps, that is 12B in 10ms, so your suggestion holds water... If we calculate in the starting bit and "\n\r" its equaling the 12B transfer in the time of the 10ms delay... I will test this first thing tomorrow...
ser = serial.Serial('/dev/ttyUSB0', 9600, timeout=0)
I set the timeout to be 0ms so if the ser.readline() fails its instantly thinking that its the end of transmission... The Python code 100% is not the problem since when I connect the Arduino Nano using the same converters to my PC using the Serial Monitor of the Arduino IDE I get the same results...