hey
without having a maximum of info you take the risk of a bad diagnosis .... it looks like a lockout of nutrients but it also be other thing a lack of calcium mg in a combo with ph variation .... if u want a more accuracy diagnosis we need to see all plant to see if it s older or younger or the whole plant .... and know ur nutes shcedule.
calcium and mag are ofentlly in lack after the stretch phase.
all i recommend to you for now is using beneficials fungus bacteria they will break the lock out process and help to regulate the feed ..
good luck