Reddish brown dots on leaf veins

Can anyone identify this?
Currently in day 18 of flowering. I dealt with a magnesium deficiency through parts of the grow because my pH spent some time in the low 5's and regularly in the high 5's (First time using FFOF). There's mild interveinal chlorosis on a couple lower fan leaves, but not really on the spotted leaves. Could this just be a progression of mag def?

I think it may be related to your prior.PH issue. To me it looks like a Mg and/or Ca deficiency.

Could it be Manganese def?

Nubcake here only on 2nd grow BUT! Someone else on here shared these so I'm just passing em on.

Calcium deficiency mentions "darkening of veins". I also have the rusty brown spot on a leaf or two so curious to see other opinions!