This keeps happening to me. The first true set of leaves keep turning yellow at around 20 days. I fed 1/4 strength top dressing about a week ago and 3/4 strength today. Roots original, hlg135 rspec,78 degrees, 58% rh. 4” intake, fabric pots off the ground. What’s going on?
They probably should be removed. That close to the soil the won't respire well and now that they are dying and almost laying on the soil it will be an invitation for bugs. Just pluck em off it won't hurt the plant.