We’ve found 2 solutions that gives us 100% seamless effect.
- Merge planar elements to one mesh. In engine (you can try hlod), or with your 3d software
- Static Lighting level scale=0.1 (+indirect lighting quality=2, indirect lighting smoothness=0.6) - when you have enough time to wait.
Good lightmass uvs are also very important - uv shells should be snapped to grid, enough padding etc.