Why are the outlines of the CC mesh I created strange?

Hi. The vertices on your mesh must have the same coordinates as the ones on legs. They must also match in uv_1 and be affected by the same bones.

- select your feet, switch to Edit mode, select the border edge on the left foot, assign it to b__L_Calf__, do the same with the right foot and b__R_Calf__;
- select legs as well, switch to edit mode;
- select every vertex on your feet's border that does not align with those of the legs;
- press Delete, choose Dissolve vertices. You can select those n-gons and triangulate them;
- enable snapping to vertex;
- select vertex on your feet; move it to snap to the closest vertex on the legs. You cannot move vertices on legs, only on your feet;
- you need to mirror uvs in uv_0 and uv_1. The skin on the left leg does not match the one on the right, so there will be a difference in textures. And morphing does not work right because of uv_1;
- feet need to be vertex painted with 00FF00.

Its a uv_1.
- expand the rig, make feet selectable;
- select them, in 3d view press Shift D, then Esc to duplicate;
- select feet.001, select soles on both feet, delete them ( important );
- also, the mesh is still not vertex painted with 00FF00;


Unrelated, when you transfer or edit weights, you should use Clean tool with all groups

Uv_1 does not work by the same principle uv_0 does, aligning it with the skin texture won’t help. It uses hot maps and that won’t help you much (toes do not exist on them).
It is just a matter of tweaking, but you could try transferring uv_1 from a custom mesh.