I've had trouble using rigid diaphragms in the Physical Modeler. When I select a group of nodes and assign them a diaphragm all at once the diaphragm produces an error in the Analytical Modeler. When I add the same nodes to a diaphragm one by one in the spreadsheet I don't get the same error when I switch to Analytical Modeling. Even so, the diaphragm seems to get easily corrupted as the model changes.