Damn... I don't know what to say except that I'm growing here in Maine myself and it HAS been a bitch of a season! And I chose THIS year to do my first-ever outdoor grow...
It sure sounds to me like root rot - but that wouldn't make any sense if the ground underneath them was dry! I know you want to learn - and maybe someone else will be able to point you in a logical direction - but you've asked the commercial grower and I'll echo what he said: shit happens... and 1 (now 2) plants in 4 years... you shouldn't be ashamed!! The humidity has been grotesque, the heat, the bugs, the fungus, the wind, the everything... I'd take this opportunity to, as you said, to spread your grow out a little bit to get better air flow through the rest of your grow.
One thing popped into my head as I was reading what the commercial grower said to you... I've just recently read a rather crazy article about how we're planting trees (bear with me) the wrong way... that we encourage them to become rootbound... that we should instead of digging a nice round hole, dig a square hole (sounds daffy to me) and KEEP THE BOTTOM OF THE HOLE SLANTED, planting the tree at the top of the little hill so the roots are encouraged to grow DOWN, not AROUND... So all of that to say, if these were clones, maybe they DID get rootbound in their circular pots and needed more encouragement to grow DOWN... like bottom watering at the beginning? Just a thought.... (and most of that thought was a little weird!)...
Good luck, man... I think we here in Maine, like in so many other parts of the world, are going to have to contend with conditions we've never had to contend with before... but onward and upward...
Good luck.....