I was updating the final piece of Unit 2 when everything went bonkers! I 'lost' the entire module inasmuch as I had already saved the sections as soon as I updated them.
On the 'Units' panel, it shows all the mandatory elements I had set up. However, the same is not true on the Unit settings page. I have included a screen shot of the Unit 1 structure
Very frustrated. Could I be looking at 3 days' work down the drain?