I had some leaves that looked similar to those. What caused mine was the fact that the power went out for almost 3 days, so they had almost no light (flashlights and LEDs, lol), virtually no ventilation, and the heat got rather extreme (99.5 at the peak of the hot days). I'm not sure specifically which factor caused the spots, but before the power outtage there were none, and afterwards there were. I'm not complaining though; I'm glad they survived that ordeal at all.