Diagnosis needed

This has happened to 4 of 15 of my plants.
They are all sisters from one batch of cuttings. The potting soil might be different for some from the others.

Magnesium deficiency due to my use of RO water and using signicicant % of coco(%25) in my mix was my initial thought. Currently using Botanicare Kind but have added supplemental watering w/PH 6.8 Cal/Mag for 5 days.

Thanks in advance

Hey dude that curled up claw thing you got going on just shouts overwatering to me. If it is let em dry out, til pots are light before you water next