Brown leaves are from the flush?

hey there ! when the leafs yellow like that it's from magnesium deficiency or even a bit of water dropplets that have collected on the serrated part of the leafs during watering then created a "magnifier effect" with the light which caused light bleaching. It's probably the second thing. Hope this helps ! 🚀

That's weird because it looks like nute burn... Not easy to identify without more progression, but I would say test your runoff. You may have already had nute burn (the leaves are rather dark) and your flushing isn't enough to clean the nutes out of the soil. So you may be hitting a late stage burn. Otherwise, check your pH in and out and watch the progression. They should be turning yellow, not brown.