The top banner (showing “FreeNAS® © 2020 - iXsystems, Inc.” at the right) overlays the vertical scrollbar. On smaller pages this is not a big issue as the “grip” is large enough and protrudes under the banner so it's reachable.
However, on larger pages, e.g. System → Alert Settings, the grip is not reachable because it's small enough to be completely hidden by the top banner.
To log banner at the bottom has the same problem. It overlays the scrollbar.