As I told you  you can play with the tangential and/or normal stiffness through commands and also the CZM parameters of your contact region in order to have zero stiffness after debonding (In my opinion its a very good agreement but if you want more accuracy then you have to do more trials). you can start with the following command under the contact and change the normal/tangential stiffness. (Mode II debonding is mainly governed by the tangential stiffness >>>hence, you can start by reducing the tangential stiffness to the range (-120 N/mm3 to 200 N/mm3) and run the simulation. (Trials >>>> check your solution with different values and see how the curve is responding to the tangential stiffness values). then if no change in results you can change the CZM parameters one by one and see how this can affect your chart (but I think the main issue is with the tangential stiffness)


Command to change Normal/Tangential Stiffness (-ve sign in the command is very important) 

RMODIF,CID,3,-2e7      !normal stiffness N/mm/mm^2 for contact 

RMODIF,CID,12,-160    !shear (Tangential) stiffness N/mm/mm^2 for contact 

Also you can change the tangential stiffness by changing the normal stiffness form ansys interface


In both ways above you can then check your contact stiffness by inserting "initial Information" under the contact tool. you can right click on any text on the table head for ex. penetration and then a popup menu will show up all you have to do is to tick normal and tangential stiffness in order to add them to the status table.