It actually wasn't nute burn. I don't use many nutes and none at all during that stage.
What happen is...I moved them to a cabinet grow in my detached garage and the temp. was way too low (1st day or 2 temps. were in 40's) so I added a heat lamp, BAD, BAD idea! Once I removed the heat lamp and added a small electric heater instead they began recovering very well.
Yes, the really bad one did make it and grew vigorously but unfortunately it was the male.