Hi @acmeek,
I just went into one of my institution's Summer courses (it has 28 students in 2 different sections, 25 graded assignments, and 8 assignment groups).
I filtered it down to 2 assignments and 4 students and used the "Export Current Gradebook View" and the CSV file that I downloaded had only the items that I was expecting (I wish it exclude all of the assignment groups and the total scores at the end).
I also used the filter option to only see students in 1 section and 1 assignment group and the CSV file was what I was expecting.
If you are not experiencing that, I would recommend that you reach out to Canvas Support directly.
-Doug