Loop cut not going all the way around object after joining two objects

Hey all. I’m trying to get to grips with lots of Blender basics, and at the moment I’m dealing with loop cutting an object.

I created an object, duplicated it, rotated it by 180 degrees so as to have a mirror of the original, joined the objects so that I can work on both in edit mode simultaneously, and merged the nearest vertices of each piece so that they are one. When I then try to do a loop cut, it stops short of looping the copied geometry. Am I overlooking something here? I have checked for duplicate vertices and faces, but I didn’t find any.

I’m noticing that loop cutting seems to be affected by how the pieces were combined together. When using new edges and new faces to combine pieces, loop cutting does work as expected. When pulling vertices from one piece to vertices of the other piece (with vertices merging turned on), loop cutting doesn’t wrap all the way around the object here. Maybe there is something more logical at play that I’m not seeing, but I guess for now I will have to be very careful of how I combine two pieces of geometry.

Have you removed doubles and checked there are no internal faces ?

I did. I even manually counted the vertices and compared to what Blender was reporting.

But I am trying to recreate the problem in a new file, and I can’t do it no matter how I combine the two pieces together. Until I might run into the problem again, I’m marking it up as an unknown user error. I suppose it’s possible that I somehow missed an internal face when looking for them.

Post the file so that others can look into it.

Select one of the 8 vertices where the loop cut ends and drag it around, perhaps there is some hidden overlapping geometry below.

I should have posted the file when I ran into the problem. But in my state of fidgeting with the problem, I didn’t save the file.

That is how I checked for hidden geometry. But I might not have tugged on all vertices.