Did you pot-up (put undisturbed root ball in a bigger pot with more soil) or remove old soil & replace with new?

I potted up...bigger pot and new soil.

I would suspect the already distressed roots weren't helped by potting up.

"Repotting vs. potting up - that there is a difference between the two
operations is a concept foreign to most hobby growers. One of the
practices ensures your plants will at least have the opportunity to grow
to their genetic potential within the limits of other cultural
conditions; that would be repotting, with its accompanying root
maintenance, complete or partial bare-rooting, and a change of soil.
Potting up, on the other hand, only temporarily allows the plant to grow
a little closer to its genetic potential before root congestion and a
diminished number of fine roots quickly returns the plant to the state
of limited growth and vitality it was experiencing before potting up." - Al (Tapla)
- http://forums2.gardenweb.com/discussions/1490818/good-growing-practices-an-overview-for-beginners?n=143  (The whole, helpful post.)

That said, it can be easier to just take cuttings of Pothos (and many other non-woody entities) than trying to rehabilitate old already unhappy roots since they take root so easily. Many people do this periodically on purpose to maintain lots of new growth at the soil line/a more full looking pot (and partially motivated by not everybody enjoying having vines creeping around the floor, just wanting to trim them instead of do some kind of trellis or the "around the ceiling the whole way around the room" thing.)

It looks like it has some kind of fungus. The blackish pattern and bright yellowness don't look like dying leaves to me. Can you take a few leaves to your local Ag. center for proper ID?

maybe check for aphids... mine had that problem before.. good luck

Chuy