Inconsistent lighting across objects/ obvious seams.

So my levels are constructed of various segments and are built by modules, but all the walls use the same material. No matter how high the resolution, with or without compression and with changes in padding... there is a clear disparity between gameobjects.

This problem is inconsistent, as with some objects the lighting is seamless, but I'm unable to determine the reason for this.

I have tried directional and directional specular lighting, using only baked, no realtime. The issue only occurs between separate gameobjects, but I cannot merge the gameobjects, due to how the game works. Any advise with how to solve this would be appreciated, feel free to ask for extra info.