Healthy stem means the framework is still there, just have trouble with the leaves right now. Need to know a couple of things: what is the ph of the soil and the water you are giving it? When was the last time you administered nutes to the plant. I actually had an issue like this on my hydro setup this morning, and everything was within limits. I went and recalibrated my ppm meter and ph meter, and I'm guessing it was the ph that caused mine because it was the only one that needed to be adjusted. Your soil moisture looks ok from here, but you want to be careful about overfeeding because it can cause the same look.