Please Identify this?

Looking like the same problem im having. the plants ive corrected were casey jones in small 1 liter containers of pro mix hp. first i moved them to a small veg tent. then watered with RO and 5ml per gallon 29% h2o2. Started reversing the yellowing after a couple days. Still not sure what was causing this problem. It doesn't look like off-gassing to me.Broad mites were just suggested as the cause yesterday. your post was the first i came across in my research. You will need a 300x microscope to see broad mites. check this out

i guess you dont need a microscope that powerful to see them. i did find this diagnostic article that was also helpful. a lot of the same information. they list forms of control at the end.

I can't really tell from the pic but what you circled appears to be scale. I have seen it on houseplants before never cannabis. It usually has little affect on houseplants but I could see them doing damage to a fresh cutting. Those little honey dew drops are like a nasty little cocoon.

What ever it was they have out grown it and are doing well. It was most concerning how quickly the onset of the yellowing and the curling of the leaves. What ever the honey dew looking droplets have not reappeared. I think it is/was the wood. Its the only change to the space or methods.

Google image "plant scale". I'd bet a dollar that's what you circled in that photo.

what was in your water (ph, ec, ppm) ? How warm was your water? How did you prep the mother before taking cuttings? What did you do after you took the cutting?