This is indeed an effect of dip filtering, and it is inevitable at late times since the horizontal resolving power of reflection data decreases with time. There are two reasons for decreasing lateral resolution. First, dissipation causes high frequencies to disappear. Second, ray bending causes the angular aperture to decrease for deeper sources. It is unrealistic to ignore this fundamental limitation and imagine that adjacent channels should have an appearance of independence.
Many plotters lose dynamic range at close trace spacing, and random noise can tend to restore it.