Tilted mirror plane for mirror modifier

I created a mesh using the skin modifier. Now whenever the mirror modifier is applied, the mirror plane seems to be titled. I relocated the axis of symmetry and origin of the mesh to the inside so that the mirrored complement doesn’t overlap. In the attached photo, the object on the left is what I’m trying to mirror. Can someone tell me what I’m missing here. Other meshes that I’ve created are mirrored perfectly fine with this modifier.

The object is rotated. Apply the object rotation with Ctrl+A

Sorry for the late response Richard, and thanks very much for the help.

It’s always Ctrl-A. :stuck_out_tongue: