Does Voxel fix this issue? If it does it’s pretty safe to assume it’s a bug, you can try messing around with different shapes and shading to try and get the same result. The best way after all this would be to place a bug request to get it fixed.
This one’s been pointed out many times after the recent FIB update. You can’t fix it if you want to use shadowmap and the only way to not have those is to switch to either Voxel or Compatibility.