I’d say this happened despite the CalMag, not because of one normal preventative dose. Deficiency damage reflects what happened in the root zone several days earlier, so symptoms can still appear after you’ve corrected the cause. Damaged tissue also won’t turn green again — judge the treatment by whether new damage stops spreading.
From the photo, though, I’m not completely convinced this is classic calcium deficiency. Calcium problems usually show more strongly on newer growth, while this looks like an older fan leaf with marginal/interveinal yellowing and necrotic patches — which can also point toward K/Mg availability or general late-flower uptake issues.
I wouldn’t keep increasing CalMag blindly. Check root-zone pH, EC/salt buildup, watering habits and whether the damage is still progressing. If new leaves stay clean over the next few days, the dose probably did its job.