Stopped growth?

Secondo me é solo una questione di genetica, a vederla sembra stare benone

I am running my first ever Northern Lights too. So from Seedsman - it's smallest plants by structure - I ever grew, my average height is about 1 meter and all 3 my Northern stayed below 50, one went absolute midget. It's genetics and autos generally tent to be smaller. At same time I run Zamnesia Northern Lights auto and that plant at least is huge as bush, not tall too. You did everything right, it's just like your brother's , sisters, cousins all are relatives, but all different. Good luck !

Im surprised the two autos have not displayed any pre-flowering traits at week 6. The plant on the left is popper looking. I've noticed though out my days if the auto gets a blasted with a heavy feed and it does not like it, or hot roots. It will just stop growing and start to enter flower, they can be real picky sometimes. A lot of people have issues with autos at times and the genetics need to be locked in. most if not all auto manufactures outsource their breeding and just put there label on it. They don't really have a choice of somethings. plus the different phenotypes of the plant can be all over the place as well. Not to shit on fast buds. but every seed I've ever grown of theirs has shown pretty big variance. big vs tall, purple vs green, pine vs berry, Its a fine plant end of the day will get you high, just don't expect perfection. Then you'll like what happens. Good Luck

Some autos just stop stretching remember they are hybrids from the already small ruderalis species. Majority of the time you get a decent height with an auto if it’s good genetics then other times you may just end up with a little small runt even if it good genetics they have a mind of their own, keep her running she may surprise you in the end.