Objects not appearing in Play


I’ve spent some time building a world with lots of objects in it but suddenly when I try to add a new object, it doesn’t appear in the world when I hit ‘Play’. The object appears in the editor but when I hit Play it’s not in the viewport or even in the world outliner.

I had no problem with objects up until this point, I had a whole scene of objects that I were visible in editor Play mode until this happened, now anything I add just disappears when I hit Play.

Any ideas whats happening to these objects?