If you ask me they don't have any food to eat.
I sprouted 26 seeds and about 3 are doing the same thing.
In my case I'm pretty sure they are just genetic weakling's
In your case I'd give it a flush if that doesn't help they probably need food.
And it looks like your over watering....the way the leaves are all droopy and slow growth.
How far over the plants is that light...the pic looks like it's too high.:stoned: