The UCL Digital Accessibility team reported that at advanced levels of zoom the notifications and messages panels obscure some content from view. At 300% the focus is on elements that are not in view. This fails on the fact that you can't visually see where the focus is currently - WCAG 2.4.11 Focus not Obscured (AA).

The agreed solution to resolve this issue will be when the screen narrows and the grey overlay is active tabbing in either side navigation bars the tab order will be contained within the sidebar until it is closed.  This will prevent unexpected changes of context and focus shifting to the main content while content is obscured.