Please help whats wrong with my plant???

So ive been growing this plant for about 5 weeks and its been growing extremely slow since the beginning. The leaves have turned the really bright green and im not sure whats causing it.
Ive been growing another one for the exact same amount of time and its like 10 times bigger

I'll guess and just remember this is an assumption.

When you transplanted the seedling it didnt have any root development and it got over watered in what looks like mulch which holds water really good and you drowned the roots stunting the plant. And since the roots are all jacked up it isnt getting nutes and turning yellow on you.

hmm well if i remember correctly I transplanted it when it had either 2 or 3 nodes and it was growing really fast before i transplanted it so that might be the case. What can i do to fix that if thats what happend? And its being grow in all purpose potting soil