Looks like you ported in a game asset, Blender cycles gets a little pissy sometimes with 5 sided poles, And it tends to get very pissy when there is poles with more then five sides.
You could try retopology or maybe relaxing some of the angles.
subdividing it… 3 times, as well as using the convert tris to quads tool helps. Thank goodness for open subdiv I guess, it’s still feasible even with a hefty subdivide.
i too have issues with smooth surface effecting the mesh shading, even on trying very low poly objects to avoid this issue ,subdivide , bevel edge split recalculate nothing solves it other than subsurface ,or if someone can help me would be well appreciated