Looks like it was too much water. It is wet in comparison to other plant in picture. Might want to add more perlite and or coco to grow substrate to provide more air to roots when you transplant. Is what is looks like to me. Good luck 🌱
What is your temp and humidity your vpd may be way off and stopping them from developing efficiently also I would add a tablespoon of worm castings as a top dressing and water in your increase nitrogen and increase root growth and that will allow veg growth which allows for photosynthesis and that allows for the uptake and the use of your notes by your plant..
Seems like it's over watering. Water less, add perlite to the soil and just water when they need. You can check the soil with your finger, if it's dry in the first 3cm, you can water them. Water every 2 or 3 days, less quantity too. Good luck!