My first thought is overwatering, but since it's so close to the other one, that seems unlikely, unless there's a reason the yellow one might be getting a lot more water or have worse drainage. It looks like there might be a sidewalk there - does the water run off that directly onto that plant, by any chance?

Any chance there's a dog involved? If they're in a spot where a dog might be peeing on them, that could explain it. Sometimes they'll just keep peeing in the same spot and just murder a plant.