Although your cannabis plant will require less calcium in the flowering phase, the element is still needed for healthy bud growth. A serious calcium deficiency during flowering can negatively affect bud growth and yields, so stick to the recommended dosage. Have you checked the ph of your media/substrate ? Calcium competes with Mg, K, and Na. If these are outta balance you could have a calcium uptake prob. To me it looks like a lock out . Check the ph of your substrate. Sub and ChAs have you on the right track.  Peace