Certified GKH Gardening Expert
Unfortunately, this can be a sign of a disease or insect damage. If the patches are large, it could be either a fungal disease or a bacterial brown rot caused by a species of Erwinia bacteria. If the patches are tiny, it could be an infestation of thrips or another small insect.
Check whether you see any small insects on the leaves. To remove insects, try wiping down the leaves with a mixture of rubbing alcohol plus a tiny bit of dish soap.