those pots are big enough...you just feed more often in coco.........Not enough root space for the plant to be able to support nutes and water to both buds and leaves. Happens all the time healthy as hell in veg then slowly dies off giving all it can to the buds. How many weeks along?
You can always be carefull and repot the plant, when they are that far along I just carefully cut the bottom of the pot off and then plant the pot and all in a bigger pot. There will be little stress.