I have had a similar issue before, I am not sure how I solved it. Here are some steps you can try to reduce the edge light:
- Decrease light intensity: Decreasing the intensity of the directional light can help reduce the amount of light bleeding.
- Reduce light source size: Reducing the size of the light source can also help reduce light bleeding.
- Use Lightmass Importance Volume: You can use the Lightmass Importance Volume to control the quality of lightmass lighting. Increasing the size of the importance volume can reduce light bleeding. (Maybe not useful here, but if you are building this is worth noting.)
- Adjust post-processing settings: Try turning of unused features in the post process menu to see if there is a cause from within there.
I am sorry I don’t have a proper solution.