Plastic domes over the heat mat with a controlled environment, a clone box. Thermometer and not to humid. With a loose fitting door eg cardboard. Healthy mums ,thick stem clones. https://www.rollitup.org/hydroponics-aeroponics/15030-batch-clones-rockwool.html
It was the cold temps that did this combined with a poor quality mother. The temp in the clone box should always be 80+ .Use domes if you have to keep temps up.
Transplant shock, you have to be more carefull. In the mean time no feeding and only water if pot becomes light to lift. Can take 2-3 weeks to recover.
You need a 1000w to get the lower plant. The light is not the cause of the yellowing its nutes built up in the pot. Flush well with 6.5 water and next time use coco and hydro nutes to stop this salt burn.