Hi Steve, one thing that is a bit odd about the object in that general area is when I delete these 3 faces here:



There remains this little tiny slivery surface here that was part of the model:




That's like a little tiny micro shelf, and those kinds of little slivery surface bits can have a tendency to mess up the object structure in various ways, those can get formed if the pieces that are being booleaned together are just slightly misaligned or skewed from one another where different planar pieces come together.

- Michael