Big random brown spots

Any thoughts on what could be causing this? On a dozen or so leaves in the middle of the plant. Topped 3 times in the last month. Should be starting the transition to flower in these parts. Prosperous? Cal-Mag? Some fungus? Other plants (not this strain) show no signs of this. Grew this strain before, stem had a purple hue as well.

Thanks

White Widow x Gorilla Glue (Sativa characteristics)
Outdoor
10 Gallon Fabric Pot with a mix of Supersoil and Promix
1/3 recommended dose of Nutri-Plus Grow with a dose of Nutri-Plus Green once/week
SW Ontario Canada