Jagged Points On Mesh I’m trying to duplicate the lower part of my mesh to the other side of the model. So I select it, and mirror it to face the correct way, I join the vertices on the model. Seems nothing is odd, but once I add the modifier, I get 2 jagged vertices appearing. I cannot figure where they’re coming from.

Thank you.
You found one of the ways of testing your mesh. Using the subdiv modifier, looking at pic 4 the verts look like they are not connected. Grab one of the verts and move it around see if it's connected. Also like Jachym said check your normals are in the right direction.