How quickly do your sinus symptoms return? If it is within a few hours then this would indicate some sort of allergy. If the magnesium is stimulating yeast growth then I expect it would take a little while (1-3 days?) before you would notice any symptoms.
Yes, zinc attracted my attention in this report too. I tried it in 3 very short trials (total 10 days). On each occasion it produced same day negative effect on my mood, including irritability and brain fog. It is quite possible that these were die-off symptoms.