What happen to them

I think you're dealing more with light stress. It's affecting the flops way more than the bottom. If it was nute burn I think you'd at least see some burnt tips down there.

Looking at diary , more like couple things If you kept watering daily, you could ruin ph of soil, that led to imbalance in absorption of nutes A week ago, only top of biggest plant was burning, so light could be too intense Watering issues could cause root system fail, rot or so Looking at bottom leaves on bigger and even small talks that you overfed a bit, clawing is visible There is no one solution, you have to review your all growing strategy