This is a visual bug, so a graphic:
It’s a bit difficult to see the scrollbar in that dropdown. The other dropdowns beside it, the moving element is grey. In this one, it seems white, and the only clue there’s anything there to scroll is that one line across the scrollbar.
And when the scroll element is all the way to the bottom…
There is no visible divider. Just a thin line on the side that’s not the same thickness all the way down.