My dad had been growing for awhile now but he is running into this on a few of his plants. He hasn't changed anything from previous successful grows. Water, soil, nutrients is all the same and fresh.
These were started indoors until about two foot tall and planned outdoor. Zone 5B. Watered daily, no water logging off soil. All three were started from seed and all the are different strain. My dad is very experienced with this but I am not. If I left anything important out please let me know and I'll get the info from him.
Outdoor? I don't suppose you live somewhere that has been getting a stupid amount of rain lately? It could be nute lockout from soggy roots.
My first thought being an avid gardener of veggies. The soil drains well, definitely not water logged.