So I have some rocbud genetics that are 17 days out of soil both are in rain science 3gal bags with ffof that was amended with earth dust dry amendments I allowed soil to bake for 2 weeks prior to potting one plant now is showing yellowing on bottom leaves also running 18/6 light cycle
It looks like a cotyledon....the first leaves you see that come out of a seed. Those almost always fade away, get a deficiency and/or shrivel and die, at least on my plants But it does look like you've maybe dried out the soil a little too much with the kinked leaves. That would accelerate the cotyledon die off, make it show signs of stress.
you plants look great. sugar leaf getting used up? I think you just had that one leaf touching dirt a few times when you watered. I wouldn't worry to much as it doesn't look consistent throughout (the yellowing)