A high soil temp can cause stunted growth.

Perhaps the thin plastic cups you are using are letting in too much heat?

Maybe this is a left over of the 'damping off' disease.

They appear healthy though on the new growth.

But yea they are tiny for 2 weeks.

My first grow did that and I was the soil heat.

Thanks for updating and I am sure you;ll get more advice.

HAPPY GROWING