If the center is a different plant but also yellowing, then it could be that the light is still a bit too close.
Feel free to raise your light to 30" above the canopy (Mine is at 48" from the bottom of my tent, but I do not veg)
The yellowing tips usually mean that they are slightly overfed, which can also cause nutrient lockouts.
I would trim the excess fan leaves, then see where you are and let them recover from the stress.
You probably have enough tops now
Feel free to raise your light to 30" above the canopy (Mine is at 48" from the bottom of my tent, but I do not veg)
The yellowing tips usually mean that they are slightly overfed, which can also cause nutrient lockouts.
I would trim the excess fan leaves, then see where you are and let them recover from the stress.
You probably have enough tops now