Modelling Repeated Load Triaxial Test.

I have been trying to model repeated load triaxial test. It's a stress-controlled test. I was able to match the loading curve but during unloading force is suddenly dropping to lowest levels. I experimented with different kp values for top servo wall and defining several unloading target levels but I did not get desirable result.
I am attaching some of the pictures for reference. Please let me know if I can do something to achieve the proper result.