This doesn’t look like a bug, but rather just an artifact of the type of lighting being used.
Can you provide some details for how you’ve set this up.
I need the lighting details panel information to see what settings have been changed for your directional light.
I also need to know the world location (XYZ) of your mesh that is causing the issue. I can then place a mesh here and see if I can reproduce and offer some tips that would better help you with this.
Thank you!
Tim