Hi Gaaldornik
>>> Still don't get it why rebuilded curves and solids extruded from them causing these problems.
As "Phiro" mentioned your "G. Grid A" curves are too dense in control points.
Also, you have some tangled points here, that I think, should be the problem. (See attached)
I've unraveled some control points to show it better.
Redraw your curves with fewer points and check again.

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