on the new blender 2.8 under development some shaders and projections of
shadows are broken .. I do not know how to describe the problem technically, I
have already reported the problem to the bug list of blender developers,
although I know that the problem is probably the mesa drivers, because on my
laptop that has two gpu, with the intel gpu the graphics is perfect, with the
gpu amd I have these problems of shading.
For a specific description of the problem, refer to this bug report
https://developer.blender.org/T56211
(the tests were done on the latest mesa drivers built daily by padoka ppa, with
the stable drivers of ubuntu 18.04 eevee shading was totally unusable, so the
situation has improved significantly)