Indoor Track - Pace but No Distance

Using a 7X Sapphire Solar.

When doing the indoor track this morning, I chose the "Indoor Track" activity and my pace started dynamically updating after I started.  The pace was probably correct and the timer was incrementing as normal.

There was, however no distance at all.  And after a few moments it asked me if I wanted to cancel / battery save.  

I had been moving the entire time.  How can I determine why the indoor track function is not actually tracking my... use of the indoor track.... and resolve?