Hey!
Alright so we can rule out the PH, I checked out your nutrients..
The other ladies look good but on this or these ones (haven't noticed if it's one or more) it seems like it could be the start of a Calcium or Manganese deficiency?
Yellow and brown spots coming up like that.
Like I said the other girls look good so maybe it's just this one that's picky or she's the first to give signs of it and the other are coming next..
Check the Calcium and Manganese ratio in your nutrients and also some photos of Calcium and Manganese deficiency to compare.
Good luck.