I had this problem with 2 of my current grow
they looked like this and it was caused by a Mg deficiency
I would suggest adding some Epsom salts at about 1/2 tsp per gallon of water to your nute mixture.
It fixed this plant quite well see...
If its not the cause it will not hurt your plants so worth a shot.
The dying leaves on the first picture were very advanced at the time of that photo but started out looking exactly like yours do now.
Hope thats the problem as its very easy to fix, and while the affected leaves will probably not recover the plant will.