Unfolding Error, Shells Being Cut Apart

[lr698]

I am currently attempting to UV a model I have just finished retopologizing. I have cut the areas I want as separate shells and made sure to add an additional cut to any cylindrical shells so they unwrap correctly.Back View of Model

Front View of Model

 However, whenever I try to unfold the shells, the process takes about 10-15 minutes. When it's finished, this is the result:Post-Unfold

Specific areas of the shells are cut apart completely, making it impossible to format the unfolded UVs. Additionally, the vertex count seems to increase dramatically.

Something to note: While I was retopologizing using the Quad Draw tool, I noticed there was a moment where I could no longer create edge loops with the tool. This problem did not persist with new parts of the model created after I realized this issue. The areas of the shells that were cut apart are the same areas that I could no longer create edge loops on.

I believe it may have happened some point after I mirrored the mesh and merged it while I was retopologizing to ensure symmetry and prevent duplicate vertices. However, I had been doing this consistently over the course of retopology and it did not cause that error until that point.

Any help or insight would be greatly appreciated!!

[damaggio]

Are all the vertices merged? That’s the first thing to check. Breaking UV edges can also happen with wrong transfer attributes settings.

[lr698]

Did a little more digging into the problem and I have a bit of a better idea of what might be causing the problem. I ran a cleanup to remove non-manifold geometry and noticed that the vertex count skyrocketed. I checked one of the faces in the affected area and found this:

 I think this may have been created when I mirrored the mesh during retopology. I did so several times to ensure symmetry. This issue persists over every single face in the affected area.

Speaking of which, I found a reliable way to identify which parts of the model are affected. I noticed that they don't have symmetry despite being mirrored, so I marquee selected one side of the model. Areas that aren't highlighted on one side are affected, which means that those faces on the highlighted side will be affected too.

[damaggio]

Good, yeah you have to be more attentive next time and check your mesh topology and vertex count display, this way it won’t happen again, it’s just a matter of practice. 
best regards .

[lr698]

Something else that seems to be happening though, whenever I try to merge after having cleanup remove the non-manifold geometry, it seems to recreate it. As in, the non-manifold geometry that was removed comes back.
Is there a way to remove the duplicate geometry without merging? Merging doesn't seem to be the answer in this situation.

[damaggio]

Zip the file and someone will fix it for you.

[lr698 · Accepted solution]

Fixed the issue. What I needed to do wasn't to remove non-manifold geometry, but to remove lamina faces using the cleanup tool. After that some errors were left over. These were just unmerged faces. The model functions fine now.