FYI 7thG, I am too having this issue. I suspect its a ph issue, I have damn near tried everything else, as this is has happened to my last 6 plants now.
I think my ph meter is faulty....I am returning it monday. It keeps saying my tap water is the same ph as the distilled water I am using, which I know is not true, I pulled up my local water info online and found the ph is around 6.0 in the tap.
It also keep telling me my soil ph is 6.3-6.5, no matter how I nute, or what I water with, and no matter how many times I calibrate it...i think its just off.
Hopefully the new one will work better, and hopefully this might pinpoint an answer for us both.
EDIT: I suspect with a proper working ph meter I will find my soil way off either way, which would explain the deficiencies from nute lock out.