One leaf doesn't equal a disease.

So, how extensive is the problem? What's the overall shrub look like?

And how much rain (or overhead water) have you had?

In more detail, the affected plants (3) are about 5 ft high, several years old and I would estimate 20% of the leaves have this spot, mostly lower down. While it has been very hot here in NJ, I think watering has been adequate, mostly on the soil and not overly wet foliage. Also most of my hibiscus plants are not affected by this pest at all. The spot or blisters are fairly uniform in size and appearance. It may not show in the photo but the blister (1/2 inch) is noticeably sunken. I just looked at the underside (raised side) of the blister with a magnifying glass and they appear to have clusters of tiny orange/yellow dots. Thanks for any assistance as I would hate to have the plants die.

tiny orange dots on the reverse usually mean rust, a fungus disease facilitate by moisture and moderate temps.