"X Mirror" editiing is not working after I applied the Mirror modifier


I am modelling a simple character, on which I want to use Key Shapes to import them to my 3D game engine.

In order to create symmetric Key Shapes, I applied my mirror modifier and then I hoped that the “X Mirror” checkbox in Mesh Option will allow me to edit symmetrically my mesh.

Hovewer, for some reason, the “X Mirror” editing works for all my objects except one, which is the main body of my character.

I just don’t understand why the “X Mirror” is not working :confused: any idea?
You can find the file attached.

Have a nice day!


character2.41-createbones-smallcorrections.blend (737 KB)