Soil. Wkly nutes, plant boost and flowertime. WW auto. Light, RH, pH, temp all good.
Kind of looks like water damage, from something getting splashed on it while lights we’re on?
Is this the only leaf that was hit?
I was thinking the same thing. @beachglass I had three or four leaves effected. It could easily have been a water splash – it happens. 
Looks like heat stress … how close to the lights are they ? Temperature?
Definitely not heat stress
Temp and lights are perfect. I think it’s water. I got a little messy the other day.