I am using pega cloud and noticed recently that the access group section is missing in the Operator rule page. But It is appearing for firstname.lastname@example.org operator and no for other operators with administrator privilege.
I have recently upgraded to version 8.3.0-M4 from 7.x.x
In addition to the above information, the pzShowAccessGroupList when rule uses Default HavePrivilege function.
This function returns true if access has been granted for the privilege.
The when condition checks whether the operetor has pxCanManageUsers privilege. So, please check whether this privilege is given for the operators where you are not able to see the access group section.