Think you hit the nail on the head in your diary
As 90% of your plant looks fine.
That 1 node looks really bad.
Maybe you should look into a nutrient that helps break down root rot and turns it v into something that will help.
Try ease up on the watering.
Let her dry out and when you feed her lift the bag up to see if she's overfed she'll pass water. But you shouldn't let it get to that point.
Maybe look into root stims or some beneficial bacteria cause it probably gets an hot in that bag. So if there is any water left pooled up and it heats up it'll be breeding bad bacteria.
Just let it try out for now. If it gets worse, you might need to go in and see what's going on.
Hope you get this sorted.
Good luck pal.