CSG flicker / missing triangles / holes in the geometry at certain translations

[golddotasksquestions]

Godot version:
Godot 3.2.3 stable, Godot 3.2.4 beta2

OS/device including version:
Win 64, Nvidea

Issue description:
CSG geometry does not seem stable, flickers at certain translations, generating holes in the geometry.

Previous related issue:
#33121

There is also a very noticeable reduction in Editor framerate with only 10 CSG boxes in the scene.

Steps to reproduce:

1. Create a new 3D scene,
2. Add CSGCombiner node as child of the Spacial,
3. Add CSGBox as child of the Combiner (floor), resize,
4. Add another CSGBox as child of the Combiner (wall), resize and move,
5. duplicate and move the wall a few times.

Minimal reproduction project:
csg_flicker.zip

[Calinou]

Duplicate of #58637 (same cause – it's caused by coplanar faces).

[akien-mga]

Duplicate of #58637 (same cause – it's caused by coplanar faces).

#74771 fixed #58637, but in my tests it didn't seem to fix the MRP in this issue, nor the one from #75862.

I don't know what's the difference but let's reopen this one for keeping track of the cases which aren't solved yet (as of the upcoming 4.1 dev 2). Confirmed reproducible as of 240ed28.

MRP from #75862: HoleMissing.zip

The very old MRP from #22988 (comment) also still exhibits a missing triangle (see screenshot in #74771 (comment)).

[fire]

Testing some csg improvements.