Variations in MATLAB plot each time the program is executed
The plots are changing i.e. you are changing inputs to the model (be it random input sequence , random channel matrix , random gaussian noise ) .. there are lot of random combinations here.. which will definitely change the plot.. you cannot expect to have same plot everytime when you are dealing with random numbers.. 
You can control with using same seed in random number generator.


Use the same seed while dealing with random numbers


Quick google search on this gave me this which you can use

https://www.mathworks.com/help/matlab/math/generate-random-numbers-that-are-repeatable.html