As the title says.

Between 1400px and 1920px viewport widths, the hamburger icon (toggle button) for toggling the sidebar remains visible, even though the sidebar cannot be collapsed at those widths.

I guess this is a mismatch between the breakpoint that controls sidebar collapsibility and the breakpoint that controls toggle button visibility, which means the two are not in sync, causing the button to appear in a state where it serves no function.