I understand that.@WildBill I was just reading about VPD on pulsegrow.com trying to educate myself about this. They said in flower it should be 1.2 to 1.5 VPD. I'm at your recommendation of 1.0 right now at 79 degrees and 58% humidity. Should I lower my humidity down to 50% to achieve 1.3?
My line of thinking is to lessen your nute uptake.
VPD drives transpiration and therefore moisture uptake from your media. More moisture uptake means more uptake or attempted uptake of the nutrients in your media........the same media you have some unknown lockout.
If we knew what was out of whack, we could make logical recommendations. I'm afraid that even compost tea or Boost or SST would load up your media with more microbes or improve root health respectfully. This could help, but it also could cause the lockout to get worse. Just not enough info available to make a logical recommendation based on facts. A regular use of Boost can lessen your need for added nutes. It can increase the efficiency of the uptake with the bacteria making them more available for your roots
How lucky are you at the rez?

You could pick out one girl and try some compost tea and/or Boost and some SST........popcorn or barley. You see removal of the spots, but you should be able to see an improvement in new growth or a slow in the progress of the problem within a few days.
I'm just trying to think of the most logical route for you to get to chop. I hope you understand this line of thinking. If not, just let me know and we'll go from there.