Inconsistent order of vertices/faces in obj files animation

Question

I'm creating old-school renderer, where I'm trying to interpolate between obj file frames.
After exporting skeletal animation to multiple obj files I see that order of vertices/faces is not exactly the same in every obj frame file.

Visual representation of 2 obj keyframes with 3 bones animated:

What can I do in Blender to fix this issue?
Or maybe there is better way to do it?

I already tried to:

• Check Keep vertex order during export
• Add Triangulate modifier in object modifiers (to keep consistent triangulation)
• Experimenting with Sort elements

but with no success..

blend and objs files attached.

Thanks.