Those are the areas that are occluded in the input images. If you look at the bushes, you can see that the front is clean while the back is a mess. Probably the starting position could be chosen a bit better.
Actually, this might be a lack of understanding, look up what gaussian splatting is.
That's not occlusion.
Occlusion can block you from taking a photo.
Not taking a photo can block you from taking a photo.
Sometimes, there are two things that happen!
Seriously, you'd understand if you actually bothered to look up what Gaussian Splatting is