have grown tomatoes in the same place for over a decade, very good soil, always return plants to soil after season , fertilize organically, and use miracle grow time release granules sparingly. Last year I didn't have the bumper crop I usually do , but was fair. I use Bonnie plants purchased from Wal-M..... I did not find this problem addressed in common problems on internet. Please advise .
This is blossom end rot.
Here is an article that will help you.
I would encourage you to use crop rotation in your garden.
Every 3 years is the recommendation, to avoid soil born diseases.
Here are some more articles that you may find informative.