I realize this thread is super old, but I have to ask Joe Fresh if you ever came to any conclusions?
It was painful to read through this thread, I literally traveled down the same exact diagnostic black hole for a full year trying to gain some insight as to why all of my plants randomly started going to shit at different times. Even worse, this took place in a commercial facility when I was handed my first full room. Although we didn't have the same symptoms, I'm pretty sure it was the same underlying problem, otherwise, I wouldn't have landed on this thread.
Long story short, different strains were affected uniquely and at different times. After months and months ( I think a year) of ruling out everything possible, we were only left with a fungal pathogen. No lab would take a sample via mail and the nearest Cannabis Diagnostic lab that had the equipment to perform a reverse RNA or DNA extraction used to confirm a virus or fungal pathogen was on the opposite side of the country. After 3 months of bugging people, we were able to get a lab to accept a sample and the results came back positive for Fusarium sp, which we kind of assumed by that time.
The best way to describe how Fusarium effects the plant is to draw a comparison to how HIV turns into AIDS in humans. It started in the mother room with little symptoms like clone-rooting-time increasing. It took 3 generations of plants showing every deficiency and problem in the book before we knew something was systemically wrong.
So as the pathogen moves on to future generations it gets stronger and it was my room that I got the pleasure of witnessing 20-30 plants in random locations wilt and die overnight in week 5 of flower. This is where I would say the HIV moved onto the full Auto Immunol attack. Fusarium attacks the Xylem and slowly cuts off the respiratory system branch by branch until it hardens and essentially suffocates to death.
Before it gets to those late stages the pathogen tends to exploit each strains weakness. I watched Gorilla Glue get light stress and Lumen or heat shock, OG's tended to stunt and dud really easy (I'm guessing because they are lanky?) Every strain went through salt build up and nute lockout.
I landed on this thread because I have an unexplained leaf severe curl on select strains within my personal space. I never saw leaf curl or "tacoing," via Fusarium, but its been several weeks of troubleshooting and I now know the hard way it can only be a handful of things before I have to conclude there is a more severe underlying problem. Because I was exposed to it so much it's obviously likely it could have found it's way back. Apparently, it can stay dormant for years just waiting until it finds a host that is stressed out from a missed watering with a compromised immune system to exploit.
Anyway, if you didn't find an answer the first time, perhaps my comparable experience may lend you a little piece of mind. I think you actually called an underlying root pathogen in your first post.