I finally found the problem. She looks much better now, but it will take me longer than expected to finish the model.
The problem was that, due to my lazyness, I used a lot of single-side polygons to make certain walls, and then in the .dat file I inverted the order of the materials and put the two-sided one on top so these walls were rendered properly. In S3D that works fine, but in the game seems like it "blocks" (not sure if it is the right word to describe it) the occlusion map.
Now I will have to come back to the 3D model and make these parts double-sided.