I decided to investigate the most recent cutscene for The New War after The Deadlock Protocol and, while within the cutscene, I used the 'Options' button to access the Navigation menu. This caused my user interface to disappear other than the 'Options' menu when the button is pressed.
Reparable by restarting the client, but something to be aware of for seamlessness in the questline experience.
Thank you for reading. :)