Mirrored objects error

I do created a building and I did mirrored each apartment , then each side to obtain a floor level.
I did exported through DAE to blender where, after I placed some light I've got what can be seen in the right bottom side…

Somehow mirroring in Sketchup with a scale of -1 (that's how is to be done) is inversing something and the correct result shown in Blender is wrongly exported !

Can you check this to see why is it happening or how could be fixed ?

With kind regards

Petronel

I know little about Sketchup but in Blender, you might check your normals.
Select your object, TAB into Edit Mode, hit N key to show side panel hit the button to show normals on the selected faces of your object.
The little blue lines point to show if the normal is facing in or out. Flip the normals if needed.

Maybe you can have a look to see better what happen here.
Please see the blend attached and what is exported from there.

Petronel

yes seen in the console … B4W WARN: negative scale for object "group_8.019", can lead to some errors
Readed that you need to apply rotation and scale for objects in blender but in my case I get cannot apply to a multi user object "group1", mesh "mesh1" aborting….

Fixed this by making then not multi user and then was able to apply rotation and scale