It may be a random spirit who visits you out of curiosity or because the spirit takes an interest in you or your family in some way. It could be that they just want to check everything's okay and that's why they're interested in visiting. It could also be a previous owner who just check by the house sometimes. Spirits who has crossed over can return but they don't necessarily return by going out from the other side but they can access the place of the living while still staying on the other side. It may be possible that the spirit leave the other side when visiting and this means they can easier interact with the physical world. I don't know if every spirit can just leave once they crossed over but it does happen.

It may also be residual energy left over from an individual known as energy memories. Its memories that spirits leave after they die but can also be left by the living.