I heard from the U Maine Cooperative Extension professionals. The vegetable specialist said that the lesion is most likely BER, and that they have seen some in their trials. And according to my Master Gardening instructor/hot pepper goddess, BER can begin developing many weeks before the fruit ripen, thus it could very well be irregular watering leading to irregular calcium uptake a month or more ago which led to the problem.
Given the very dry early summer we had, I am not surprised. Even with the moisture retaining mulch, I suspect some of the plants got too dry especially given my intensive planting techniques.
I love referring to my inability to toss a viable seedling as my “intensive planting techniques.” Behold the power of words.