If the Gradebook window (the one you get when clicking 'Launch Gradebook' from a class) is too narrow, and then you access your gradebook settings (More > Settings), the left pane with the settings tabs will be completely absent. If you already have the settings page open and you gradually resize the window, you can watch the UI element disappear completely when it gets small enough.

When I say 'too narrow,' I don't mean it's actually very narrow at all- the threshold, from my testing, is 860 pixels horizontally. Even on a fairly standard 1920x1080 monitor, that's just shy of half the screen. On some machines, the gradebook opens smaller than that by default, and I've had teachers who were entirely unaware that they were missing three whole tabs' worth of grading options- they just thought the gradebook settings were weirdly limited.

Obviously you can solve this by just maximizing the thing- IF you know that it's missing in the first place, which not all users will. But this just can't possibly be intended behavior. Surely the tabs should move to the top instead of becoming completely inaccessible.