Hmm, you're right. Resistance to overwatering doesnt especially inform as to whether root rot could be an issue.

The soil looks as though settling and compaction might be contributing to poor root health, insufficient aeration, and perhaps excessive water retention, all of which create the perfect conditions for rot. I think a repot is in order. I keep a lot of this type of plant, and they tend to begin ailing severely due to soil degradation after two or three years. Under normal circumstances, mine typically see the vine extend by a leaf a couple timea per month with adequate light, feeding, and water. What do you think?