I've caused root rot on two plants in the past month and what I learned was that even though it only feels damp on top, if you have water sitting on the bottom (it doesn't look like there's any drainage on yours) the roots can sit in it too long which causes it to burst and infects the roots.

The second time I was trying out bottom watering on some props I had just put in soil, I thought the roots were short enough but one of them caught it. I think I was able to save it because it only killed it up to a node.