Lighting keeps breaking between closing and opening levels.

Hi all,

So i’ve been working on an apartment block, things have been going well and i’ve just been bringing in the basic elements to try and iron out any problems.

When baking my lights, they look perfectly fine, the mesh is a nice, clean white like i expect.

However, when i save my scene, and come back to it, it has either made the mesh fully black, or things it is from a separate section of the UV. Is their something i am forgetting to tick that is doing this, or is this a known bug?

I’ve had this a couple of times in various projects, and it would just be good to pin it down to something!