It's actually happening to all of the same type of strain. It's Space Monkey by Bodhi Seeds. Some worse then others but the picture is the worse ones. Will they grow out of this?
I could be that one strain is more resistant to whatever stressed it.
The new growth will tell you if it grows out of it.
Most likely cause was the light was to close to soon.
Low humidity or high heat would add to the problem so make sure those are in a good range.
Edit: make sure you have some air circulating.
Eventually you will need to also ventilate the air but for now you don't want a fan pounding the leaves you want just some type of air circulating. I circulate by letting a fan blow air between the light and the canopy but my lights are HID and there is much more room.
Lack of air circulation would have also contributed if there was no fan.
. But not adding Cal Mag to RO water definitely gives you little brown spots that's from my experience. But like you said there's always different variables for every grow room.
