What is a non-manifold vertex? I am experiencing a lot of issues with the topology of a specific object I am modelling. Currently I have an issue with 'non-manifold vertices on it as shown by the screen shot below:



The mesh issue I have highlighted is found by operating Select&gt;Select all by Trait&gt;non-manifold and checking only the 'vertices' option in options menu as pictured in the bottom left of my screenshot.

I would specifically like to be able to identify what the tool Select all by Trait looks for when the 'vertices' option is selected, so I can better address my topology problem

I have read a fair bit about what can cause non-manifold geometry but simply non-manifold 'vertices' doesn't really mean a whole lot to me, can anyone shed any light

Here is the blend file: 

N.B: I have recalculated internal and external normals as well as 'merged by distance' multiple times which doesn't seem to do anything
For anyone else with this problem the detailing of this is actually outlined in the blender docs here
The docs say:

Vertices:
Selects vertices that belong to wire and multiple face edges, isolated vertices, and vertices that belong to non-adjoining faces.

In the attempt not to repeat the good descriptions that exist elsewhere on this stack:

Wire edges: What are wire edges?
Multiple face edges:



Isolated vertices: https://en.wikipedia.org/wiki/Vertex_(graph_theory)#Types_of_vertices
Vertices which share non-adjoining faces:


N.B: if you hover over each option in the Select all by Trait menu you get a tooltip about each option:

This is all my best answer as to each scenario, if edits are required please go ahead