Ok, only reason I mention to wet, you explained first paragraph sentence 3. Even though coco drie fast, you have to still watch seedlings and young plants with it. When you stated soaked, it makes me wonder if inside the pot there's alot of moisture yet that the plant cant handle.
Is your system 24/7 or timered?
When you go on to say daily 10% runoff I ponder even more.
I have used coco, hydroton, lava rocks, dirt, perlite straight, for grows.
Knowing the dry inside not top surface, and wet inside is important. If your watering as you explained, and literally dumped soaked soil, you may have to much water.
Stick your finger in there and see if it feels wet. If so back the watering off. if not, my bag. Just trying to help.
A cheap moiture meter may help as well as next time scale the smart pot full and wet. then scale it dry. If need be write the number down and length time to dry. I forget shit all the time.
I have seen plants take well to overwatered situations. By this I mean they appeared healthy but no grow. As soon as water was made less available I seen them fly in growth.
I wont go into detail, but an agent orange pulled some real crap with water with me, it almost liked nothing for water.
Hopefully you get it sorted out, best wishes.
