Shadow artifacts on HighResolution Rendering (Tile rendering)

Hello,
I am trying to produce an 8k render using HighResolution Rendering (Tile count set to 6). But I am getting strange artifacts with shadows as apparent in the attached image (Rendered at 4k for testing). The one without High Resolution Rendering on renders without any artifacts. Will be great if someone knows the correct answer.
Regards

The differences in the left part are clearly visible, but other differences are not that clear. Can you post both pics separately ? So we can compare them 1:1.

I have discovered the cause of weird shadows. Enabling hardware raytracing fixed the issue.