Stem narrowing, I have no clue about the cause, please help (don’t take into consideration the burnt cotyledons, that’s another story)

There are various symptoms associated with damping off; these reflect the variety of different pathogenic organisms which can cause the condition. However, all symptoms result in the death of at least some seedlings in any given population.

I agree it could be dampening off, I don't see the rot at the base of the stem but the tapering is a tell tale sign and falling over, and even if they pull thought the damage has been done and the plant will be lesser then. I would recommend using a sterile seedling mix to start them off in and keeping the air flow up. I'd also use good bacteria to out compete the bad ones. some-like like adding in compost or a additive like lacobacteria. I've read mixed reviews on the cinnamon trick, not to say it does not work, I just don't think it works as well as some of the other options. Good Luck!

Das nennt man Umfallkrankheit und wird von einem Pilz verursacht. Das tritt häufig in Verbindung mit zuviel Feuchtigkeit im Substrat oder zu hohem RH. Der Pilz kann aber auch schon vorher im Substrat sein. Um die Umfallkrankheit zu verhindern, kann es helfen ein wenig Zimt oder etwas Wasserstoffperoxid (3 Prozent) um den Sämling herum zu verteilen. Dies wird den Pilz abtöten. Happy Gardening

Thank you GMSgrows, yes I knew about these method, but I wanted to understand the cause of this bottleneck forming, or maybe it’s just random? Also, for now it only happened on FastBuds’seeds, but I don’t think I had many plants with other seeds producer to make it a proof and I don’t think that is the cause. In the end, yes the baby it’s probably gone, she’s not following the sun anymore :( I already put another Moby dick auto seed into germination

Try sprinkling a little cinnamon around your girls and water in after they sprout. This prevents damping off. You can also get a product called nodamp from the nursery. It may be to late for these ladies though.