Deficiency

Feed it calcium. You always need it. Not as much in flower as in veg but if u lack calcium from the beginning you have troubles. So give it calcium maybe so magnesium as well but not super much. And you will be fine my dear friend ☺️

obviously not. When you encounter an obvious contradiction to 'bro-science', it's time to let go of the bro-science. Definitely looks like Ca deficiency and it's been going on for a bit. If not enough Ca in your soil, you need to supplement it at all times. So many things out there are just total nonsense that people made up and repeated so often that it became 'truth' to the subculture of pot growers. Whoever told you Ca is not needed at any particular point in the life cycle is a victim of this phenomenom. Same with those that think you need little to no N in flower. that's insane if you know the structure of nucleic acids and other components of plant cells. It is needed for a wide range of things above and beyond stem elongation and leaf growth - i.e. 'vegetative' growth. Go check out guides and articles on cocoforcannabis.com. rid yourself of bro-science dogma.