@droftarts I was using a prefab stepper wire and stepper motor from another printer that was working normally for testing. I believe the motor is 1.33a rated.
I hadn't changed anything in the duet settings, so it was whatever the default values were.
On the subject of the voltages, I was monitoring them with a multimeter after the motor failed to move normally. I had 24v at the board input terminals, but I was seeing 16v in the duet interface on my laptop.
I checked the wiring was correct at the time, but it was a few weeks ago by this point so I can't remember the specifics, and I've been working on the alternative control board for the project in question so my head is full of marlin now unfortunately.
I honestly don't know what went wrong, I just want to get the board fixed, whether that be via warranty or paying to have the driver chip replaced (provided I can confirm no other faults on the board).
Working with marlin now or reminding me why I opted for the duet on this project to begin with.