The linked PR adds new buttons to the assignment submission navigation options to allow the maintainer to not only traverse linearly (original buttons), but also to allow to move to the 'Next/Previous Ungraded' assignment, as well as a new checkbox which applies to all 4 navigation buttons to traverse only those students who have submitted something for the assignment.
The linked PR also addressed the following related issues:
- next/previous being limited to paging size rather than entire collection of submissions/students
- updated messaging to reflect new navigation panel/options
- disabling of controls and activating spinners on several UIs (and several components within each UI)