I had someone take a look at The difference between the two classes and in the section id region_main, it is missing the class = "has_blocks mb_3". This section calculates the width (100%-280 pm). So same Moodle production site, two different courses, same theme, one is fine, the other isn't. Took at look at all of the setup options for the Gradebook, and they are identical.
Gradebook
Grader Report Pagination Control
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