Normals are fine. Mesh is triangulated. Surface is flat. (these are the most common answers to that problem, but not in my case) You can see it at the screenshot below. Picture: object mode above, edit mode below. You can see that the inner (smaller) cylinders have less faces, and the outer cylinder (larger) has twice as much (I did subdivide it). I can assume it is relaed to that subdivision. I have made subdivision (selecter upper and lower edge of cylinder and pressed W - Subdivision)
How to fix artifacts in Blender
Mesh - weird shadows - CG Cookie
Strange selfshadowing artifacts in Cycles - Technical Support - Blender Artists Community
Weird shadow or whatever this is - Modeling - Blender Artists Community
Cycles volumetric scatter makes strange artifacts on plants - Lighting and Rendering - Blender Artists Community
8 Tips for Clean Topology in Blender (Updated for 2021) - CG Cookie
Odd view window artifacts. My model appears to be deteriorating - Modeling - Blender Artists Community
Creating 2D Sprite-Based Retro Worlds
bevel - Strange shadow artifact in viewport and render after beveling the corners of a boolean cut in mesh - Blender Stack Exchange
Low Poly Artifacts in Blender Cycles (Terminator Artifact)
Imported mesh from blender has shadows artifacts : r/unrealengine
How do I fix these weird artifacts? -Blender - Building Support - Developer Forum
Weird shadows when extrude from circle mesh - Modeling - Blender