I ran a across a small issue with the PermissionSet and PermissionSetGroup objects in regards to the label.

When creating a PermissionSetGroup, a corresponding record is created on the PermissionSet object.  The MasterLabel field from the PermissionSetGroup is copied on the PermissionSet record into the Label field.

The issue is that if the Label (MasterLabel field) on the PermissionSetGroup record is updated, this update is not reflected on the PermissionSet record, it still holds the original label.  The PermissionSet record also cannot be manually updated/fixed as being related to a PermissionSetGroup record this is not allowed.

I ran across this with some custom tools that we've developed, it's something I should be able to work around, however wanted to mention for awareness.