From what i've seen, these
plants are very touchy about being moved, repotted, fertalized, and being located. They don't die, but they get awefully stressed. Their leaves go limp or die, and stuff like that. I have one being rooted in water right now, and ever since i cut it from its parent, its been all limp, and stressed. Its still alive, so i put it next to my ficus, and it climbed right up it lol. Did the whole "i'm gonna root myself here" thing too.
The middle of your pothos doesn't have many leaves probably because it doesn't get as much light in the middle, or its concentrating on getting light from the leaves on the outside. I'm not sure ^.^ They're nice
plants though

Maybe someone else will know more