I burned my ladies roots once adding too strong a dilution of H2O2 to my soil. (I don't do that any more) The leaves kinda looked (and felt) crispy, and looked just like yours. But since you mentioned none, I'm guessing that that isn't it, lol.
Does look like some sort of lockout, but doesn't look like the ph lockout I'm used to seeing.

I'd give what rhizome said some serious consideration. You might be over-micronuting them.
Any recent changes to your micronutes or their schedules?
Have you been attempting to foliar feed (or micro) them, in hopes of a recovery? (spraying stressed plants...?)

p.s. Nice molecule...cannabis perhaps?