This may sound weird but I am sure the Delete node was actually deleting the filtered line and fill patterns yesterday. Ironically, when i went back to test them again, the dynamo flow seems normal and shows that 21 Elements are deleted but when i check in the revit file those elements are still there. No matter how many times i run the flow, the result shows that the elements are DELETED but no effect on the revit file. I was able to do it yesterday though. Bizarre.
Sorry if I am missing something very fundamental.