In my experience, FFOF is not too “hot” to cause those issues with nutrients alone .
Are you 100% sure your pH meter is reasonably calibrated? I found my meter had gradually gone completely out of whack and was reading 0.8 pH too high. Which means in reality I was pHing down to 5.5 in some cases. Way too acidic.
Being an auto I would not get expectations high for the plant that got sick. I expect you will save her…good advice up here…but yield will suffer greatly. Can be some fire smoke but in my journeys with auto a bad start stunts them. Just my opinion only and probably wrong. I never pullem unless they die or are males. Good learning plants when sick.
Update on the Wilted seedling or the “SICK “ one. It has recovered, I think, nicely. Some funny leaves at the spots they were before but sprouting new growth and leaves. They are pictured left to right, wilted one far left. I really did not have a overwatering situation imo…I e had some issues with each Zkittles seed I’ve started, one turn male, the other died after transplant, with no obvious reason. So maybe a bad batch of seeds or bad genes. Anyway, I won’t buy Zkittles any more unless this one has a good recovery and yield. Thanks for the advice