There's a root pic in my donkey dick log but you still didn't say what you transplanted into. Did you just put the peat puck in a cup? You need actual medium in there- soil or soilless- to qualify as a true transplant. I think you very likely had too much water in the peat pellet or too little oxygen to the roots after transplant.
Here's how I do it- when I see roots, I transplant into a ~3" pot that has nice FLUFFY, LIGHT soil in it that drains real well, and water the soil only VERY lightly. The roots need lots of oxygen when they are growing, and too much water or too dense soil blocks O2.