I've been running BPN for a couple of years and have not had any problems like this. However, I grow hydro. You may have multiple deficiencies. I know BPN has all the macro and micro nutrients you need so my guess is something is causing a lockout.
My suggestion would be to first check the pH of your soil. You want it as close to 6.5 as possible. This is the ideal range for nutrients to be absorbed by the plants. Also, are you checking your pH of your nutrient solution before watering? What has it been? If not, you really ought to get you a meter and start doing that.
Now if you have been doing that... what kind of water are you mixing the nutrients in? If its not RO or distilled you may want to switch to that. If you have lots of calcium in your tap water, like I have, it can bind with some elements in the nutrients and form new compounds that plants are not able to absorb. Which is something else to pay attention to, the way you mix your nutrients. Be sure to add the nutrients to water, never let the grow micro bloom mix together unless they are already in your gallon (or whatever size watering can) of water. if they combine in concentrated form some elements can form insoluble compounds and cause lockout. If all your pH and water is good, then I'd probably just flush with RO or distilled water for a few days and then reintroduce the nutes.
Other than that man, you can join the BPN Army here on roll it up. Its a group on here made by some other BPN users, they might be able to help, but I dont think your issue is BPN specific.
And then there is this guy, Skiya, seem super knowledgable. He just started using BPN, he may offer some good suggestions. Go to his journal see his garden. Super lush and green. Message him and ask him to come see if he has any suggestions. Seems like a real nice guy who likes to share his knowledge.
https://www.rollitup.org/grow-journals/731315-blue-planet-nutrients-journal.html
Best of luck to you buddy, you know you got lots of support here at ROI so keep reaching out. You'll get this issue resolved.