Its not the cal mag thats suspect but the type of cal mag. Its likely nitrate or sulfate based, not carbonate. So no pH buffer...
Here's what this idiot yours truly thunked up.
Hes been feeding with terpenator, cal mag and molasses in a good balanced soil. I think terpenator is for flowering? Ive never used it. But if its a high potassium like a 0 0 22 being used so frequently and maybe in veg, it could be acidifying the soil. More so with the other acidifier molasses. How much uptake of nutrients happens at less than even 6.4 ph? Calcium could be functionally deficient due to pH as well as potassium cation over saturation. No matter the liquid source of it. But the carbonate form, dolomite lime can also correct low pH and help flush the potassium away. Make sense? The RSO is kicking in lol