You're not given any context when you tab into the task.
Also, you're not really able to solve the task in NVDA because you're not in 'forms' or 'focus' mode so the keyboard events for the arrow keys don't work.
Add role 'application' or similar to the task wrapper, covering only the part that we don't want "explored" where we use our own key handlers. Add aria-labelledby that references the task introduction or instructions field on top.
1. Give context to the task when entering it.
2. Let the readspeakers know that the arrow keys have custom event handlers.