That may have been a little bit of an excessive watering/ soil too strong... And with all the amendments in the soil it just steeps tea in the saucer underneath. I’m glad I got these saucers incidentally. They really help you see how much water your putting through, and there’s nowhere for it to go so it’s helping me dial it in better. The plant certainly absorbed all that water in less than a day, but it may have been a little bit of a strong brew.
I think I will just dial back the amendments and add that dolomite lime for future transplants and see how that goes. I have definitely got a feel for the watering frequency vs pot size&root mass size. i.e. evaporation vs absorption. So I will hopefully continue to see better results with my next seedlings.