I have had similar spotting on my plant as well.
My best guess is because it's been a wet year here, and apparently where you are as well - that after rain the sunshine comes out and magnifies the water droplets and burns the leaves.
My idea for a solution would be to find some silica powder and feed/spray it on the plant to promote thicker foliage.
I learned this from KaliGrownBudz on YT:
RE: Little up-date of the Organic Outdoors!