Roots have been mentioned once or twice, and I fully believe they are your problem. I've ran into this issue before, it makes you think it's a nutrient lockout of some type or whatever...and it is a nutrient problem indeed, but it's because your roots are probably trashed. Since the roots can't property uptake nutrients, the plant is effectively cannibalizing itself to get the mass nutes it needs to build the big buds you want. I almost guarantee that if you uproot that sucker right now (which would be insane...don't do it lol) you would see the roots would resemble an elephants foot (sorta). There would be a fat mass below the base of the stem with spindly shitty looking roots coming off of the rotted nasty fat root foot. It'll still make buds, but expect about half the yield you would have gotten if your roots were healthy. Number one cause of this condition is overwatering and nothing else. Not saying this is 100% what's happening here, but I've experienced this and that was indeed the culprit. I attached a pic of a past plant that had this issue. See how shitty and sad it Is? This was 7 weeks into flower, and it pretty much looked like that since week 4. After harvesting, I pulled it to see if my assumption about the roots was correct, and lo and behold, when I pulled it, it looked like a ginseng root....no bueno.
