Lighting Glitch

Hey there.

Ive started getting a weird lighting glitch recently in one of my projects. I never made any changes to objects related to lighting but for some reason when you look at certain points on the terrain the directional light from outside shines through the roof. The video ive added explains it better.

I don't technically need the light to be on until I exit the cave so I could just trigger it on at that time but Ive never noticed the issue until today. Any idea what might be causing it?