I OVERDOSED on calmag 2 days ago - today I got the SAME leaves as you (It is very likely a PH problem). I overdosed because my calmag is organic and my PPM meter was showing wrong values, I didnt know PPM meters dont really work with organic nutes.
My plants are autoflowers on day 15. I am waiting whether th yellow spots spread. If they spread, I will flush with RO water.
P..S I am a total newb, but I looked in many forums for why my middle leaves have yellow/greyish patches - PH issue was the most common answer