Select one of the top tiles, enter edit mode select all the verts, de-select double sided and set smooth again.
I have run into this before, why it happens I don’t know, but now I never have any of my meshes double sided if its going to be smoothed.
image with one tile changed:
Is it possible to lock an object, so it can not be edited or moved?
You can do this with scenes – see the “Set scene as set” https://blenderartists.org/forum/viewtopic.php?t=31182&sid=f7a7ccd2986fa6e70443ecf07f388a75
Add a new scene and set the original scene as a set in the new scene. Then the object from the first scene won’t be editable in the second scene.
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