I am growing two autoflower seedlings on my balcony in sunny Mexico in soil and very little organic fertilizer. Two plants in identical conditions started at the same time but one is noticeably outgrowing the other. Why does the White Widow struggle and the Deimos thrive? Here are some photos after two weeks since popping, obviously the smaller plant is the Widow.
Its called Genetics. A perfect example is two parents have 5 children. The siblings generally look different from each either and take whatever from each parent in genetics.
Nothing to be worried about.
Except for that “soil” they are in.
Too heavy, compacted and clayish?
Soil looks like you have possibly over watered them soilis indented and cracked