Its your heat mate.
28c isn't ideal for cannabis plants in that stage. In ripening lower the % of your light so you don't get too much loss of potency. As a lot less ppfd is required. Also, ventilation will curve a lot of this.
Idk what your ambient co2 is, but you're nearly hot enough where an exhale co2 bag or something would be of great benefit to you. But, extra ven and make sure all your plant is been kissed by wind from a fan at some point.