QPSK Transmitter and Detecter

Hi, 

I have tried running the QPSK transmitter and detector examples on simulink and 9/10 times it does not work. There example is taken from mathworks: https://uk.mathworks.com/help/supportpkg/plutoradio/examples/qpsk-transmitter-with-adalm-pluto-radio.html

I do run the frequency calibration simulink files to calibrate the transmitter and receiver. Does anyone konw what is going wrong? Also would anyone know how to implement a much simpler version of this transmission where only bits are transmitted using FSK?

Thanks,

A