Sorry to hear. I would get some bag seed to practice. Sounds like drowning or pythium. Some times what is suppose to be simple can throw us for a big loop. The last couple times I started from seed they germ fine but then I forget in a few days and give them nutes with everything else. Not pretty to watch them yellow in a few days. My bro-in-law just wasted 30 plus cutting he was going to root. Not one rooted for him and he was trying dif methods. the same cuttings I rooted 46 out of 49.

Almost sounds like the seed was cooked. A little too warm and it's all over too.

Lately I have been starting in rapid rooter or root riots. Just like rockwool you have to watch and not leave them too wet.