In the last few weeks, the plant has begun to struggle. A lot of its leaves are beginning to bleach/yellow, and eventually shrivel up and die. I didn't realize how big a problem this was at first until I checked the underside of the vine and noticed that a large number of small leaves had withered away without me noticing. As for conditions: The plant sits in the corner of my room adjacent to a south-facing window, but in a way that it doesn't tend to get very direct sunlight. It's been in the same place for several months, so if the issue was too much sun I would have expected it to become a problem in the summer instead of now.
I keep the soil consistently moist, I am a bit worried this could be due to overwatering but I believe I've seen the results overwatering in this plant before and it looked different than this.
The heat in my apartment has been on for the last two months, though I only started noticing these issues with this plant in the last two weeks. I also keep a small humidifier running in my room at all times and the humidity tends to be at least 40%. The plant is somewhat close to the radiator though (its built into the wall under the window).
Anyone have any idea what could be wrong with this plant? I'm starting to get worried about it.