A few suggestions:
- Move the directional light out of the area of the depicted hallway. Currently it is immediately above the ceiling and inside the doorway.
- Change the directional light’s Environment Intensity to 0, even though the color is black and invisible (0 alpha). It could be still generating light bounces from the outside skysphere / environment and contributing to the light leaks.
- Check post process volume settings, especially under Rendering Features. What is enabled (checked)? What are the auto exposure settings, even if they’re disabled? Modify those to decrease exposure. Decrease global illumination, and in Light Propagation Volume, decrease intensities and occlusion to see how it affects that scene. If it causes the light leaks to get worse, then increase occlusion and modify bias settings to see if it reduces or removes the leaks. So in keeping with this, ensure the camera is viewing the hallway while tweaking. And build lighting only for each change or few changes.
- This is a last resort in a way. Go to World Settings, change the settings for volumetric lightmap. Decrease detail cell size by as much as half or a bit more, increase memory brick size to as high as double the current value but not more, and try tweaking the spherical harmonic setting (default is .003, so increase it to UP TO 0.2 or 0.3 and see if it removes those lines or leaks). This is a last resort because it really shouldn’t have to be changed from the default, and can affect the entire level or other areas more dramatically if done to the extreme.