I’m guessing the 1.3ph is a mistype
That looks just like what I had on 3-4 plants last grow…they all died a quick and horrible death. My only conclusion at that time and now was root nematodes.
They looked like this and it happened within a very short time like yours.
I tried flushing them with water then with Azamax and water mix then Hydrogen Peroxide water mix and so on and nothing worked.
I’m not saying it is root nematodes but that’s the only thing I came up with. Also it was right after I mixed up some Alaskan Fish Fertilizer 5-1-1 and fed them so not sure if that went bad or what but I don’t use that stuff anymore.
On a positive note another one had that same look at the same time but only partial like yours looks and it ended up recovering on its own and I did harvest her.