It looks too random to be anything systemic... a nute splash or other physical problem is probably the cause. Most plant problems can be seen in the veins or colors of the leaves and it is seldom in a patch on a few adjoining leaf lobes. I think you are fine.
do your routine - check temps, humidity, ventilation, general growing conditions, nutrients, pH, bugs, etc.... determine if it's isolated or its spreading....
do your routine - check temps, humidity, ventilation, general growing conditions, nutrients, pH, bugs, etc.... determine if it's isolated or its spreading....