New issue and not good news. As I add detail in one location, various items are disappearing in other areas. I’m not sure of the cause but I’m missing walls, wall details and flights of stairs. Nothing unrecoverable (copy/paste existing components) but I am changing my approach to the model which is to build by feature. In other words, create a separate file for each feature (e.g. separate files for Stairway E, Stairway D Miships Lobby, select staterooms etc.). Will see soon if this approach overcomes the problem.