On some pages when tabbing through the page the keyboard focus disappears and then magically reappears.
Disorienting to users when keyboard focus disappears and then reappears.
Disappearing focus is usally caused by links or form controls that are rendered off screen using CSS position="absolute", top and left properties.
If links or form controls are not visible they should be hidden using CSS display: none or using the HTML5 hidden attribute, so they are not part of the tab order of the page.
In general if you can't see a link or form control visually, the screen reader or keyboard only user should not be able to interact with link or form control.