If a CC user clicks on a workflow in his To Do list the workflow approval page opens and he can see data he has no permission granted, i.e. salary data.
This is expected behaviour. That is how it is working by design.
If you do not want the CC User to land in WF Approval Page of a Completed WF Request, please set the property "Redirect CC User to Workflow Approval Page" to 'No'.
Doing this, the CC User when clicks on completed WF Request would land on Employee Profile page where RBP would be effective.
KBA , LOD-SF-EC-RBP , Roles & Permissions (EC Core only) , LOD-SF-EC-WFL , Workflows - Configuration, Tools, Objects & Rules , Problem