What happened here?

I would cut them offf dry them and test the Sample. You cant undo the problem. The rest of the Girl Lools Healthy.

I do not know what happened but those stems are dead and dying. Green stem below with brown and crispy stem above is not a good sign. Looking at other photos in your diary it looks like some nutrient burn. Also, are your pots 1.3 gallon (5 liter)? If so that is pretty small. A adult plant in that size container is going to need very regular attention to keep watered and the proper fertilizer level. It is one case where a large pot makes growing MUCH easier. The large mass of soil acts like a cushion and is great for smoothing variations in watering and nutrients.