Why can't I make a vertical loop cut on this object? I'm very new to Blender. I've got a cube object which I've manipulated with intrusion and extrusion. I'm now trying to make a vertical loop cut, but it is only being applied to the inside of my object. Horizontal loop cuts work as expected.

I've had a look at other answers and tried removing doubles, recalculating normals and had a look for any N-gons, but as far as I can tell, everything looks okay.

What can I do to make the vertical loop cut work?
To answer my own question. There were hidden doubles in the object. Even though the original post says that this was already checked, I removed doubles again and that time it worked.

In edit mode I deselected, then reselected all and used the remove doubles tool.
A, W, Remove Doubles.

Making sure to set my Merge Distance greater than 0. After that, I was able to add a vertical loop cut.

The other SE questions I used to help fix this were:


why does loop-cut-and-slide ignore some faces but not others?
Loop-cut won't go all the way around
Loop cut interrupted