While we all have different environments, the fact of the matter doesn't change that your issue is burn. Maybe you got a bad block who knows, but that is 100% for sure not a lighting issue. Those seedlings are burned. Our experience is what we are offering you. You said you have tried everything...but changing your medium, I realize you bought the "good stuff" but even the good stuff, ffof, happy frog, black gold, super soil...ect will burn the shit out of a seedling. Continue what you are doing if you want to continue to blow through beans and not more than 2 leaves on them....Or take some advice and start them in smaller pots, in a neutral soil...like promix. Then transplant them into that hot coco you're currently using and be successful.