Quite frequently I see questions relating to new task level custom fields added to the My assignments view on the Tasks page or the Timesheet views don’t show the custom field values set against the tasks. Similarly, new resource level custom fields added to the Summary view on the Resource Assignments page don’t show the custom field values set for that resource. This is usually due to the the custom field settings, the setting in question is the “Calculation for Assignment Rows”
Set this to Roll down as displayed above then you should see your custom field values populated in the relevant PWA views.
For more details please see the following MSDN article.