I ran into an annoying issue today that perplexed me for longer than I care to admit. The fix was also annoyingly simple and I'm documenting it here so that someone else hopefully doesn't fall foul of a lost afternoon to this as well.
I run OctoPrint on a Raspberry Pi connected with a USB cable. If you are doing this you must ensure that Settings -> RPi [off] is set. I guess I must have knocked this to [on] whilst tweaking my LiveZ value (which is the next menu item down).
That's it, happy printing.