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.
Many thanks for posting on the Ideas portal. However, this issue is not really an idea, but clearly an issue you have experienced which should be addressed though a service ticket. If you are still having a problem with this please log it using the Service Management which is easily accessed using the link in the Connection Client utility.