unwanted zoning of 3D mesh above v3.6.2

• Concern : API/UI
• Platform : macOS/Linux/Windows
• Problem Description : inverted mesh present 'zones'. This does not happen in v3.6.2 but well afterwards.
• How to reproduce it : invert examples/dc-3d-timelaps-column with compile v3.6.4 or master

@jamyd91 do you have an idea? Is it something in reordering the mesh or maybe in the mesh generation that creates zones between rings of electrodes?