Overwatering is the most likely cause then. Your soil isn’t hot enough to burn them and if not feeding, then is isn’t nute burn.
Seedlings tolerate dry soil far better than wet soil. All a seedling has is a sole tap root. Roots need oxygen, and a single tap root can’t extract oxygen from soil that is constantly wet. Cannabis needs wet/dry cycles throughout its life for good root health.
In fact, seedling extracts most of it’s water from the air through the first leaves. I’ve accidently dropped a cup with seedling, put seedling back in media and it never stopped growing.
I agree that likely overwatering is the cause.
Here’s a suggestion: dampen your media before placing sprout in it. Before putting media in pot, squeeze the media in your hands until almost all of the liquid is pressed out. Use that to plant your sprout. Use a dome. Mist once daily the dome until plant diameter matches the diameter of the pot, then transplant.
That’s where I’m at. Just killing seeds. I just gotta keep at it till it works. I know I can. I have had some amazing grows in the past. I’ll get there again with help from all of you!
idk if my info will help you but I had the same problem I went to the dollar store they have these coco flat bricks I transplanted my crispy babies and only fed them water Poland spring to be exact it was already pH to a 7.5 I bought a saucer and fed them through the bottom instead from top and two weeks later the change was remarkable at this point you have nothing to loose it can’t hurt them give it a try and let me know