last 3 pictures are illustrative. View color difference of the object from the outside and inside. Material and Light meters . are the same in both adjacent objects . Last is a mapping object .
The color differences may have something to do with lightmap uvs, you generally want the edges of your islands to snap to a grid line. Try that and see if it solves that issue.
I’m referring to the lightmap UV, the edges of the islands should align to the grid. The walls seem to be static meshes, if that is the case are they modular and put together in engine or exported as one piece?