Was it stuck at some waypoint in the middle of the route?

No, it was tracking my path and correctly displaying the waypoints in the correct order when I observed this behavior.

The number in the top right corner is not an 'as the crow flies' distance to the destination, but the true sum assuming that we will have to pass all waypoints including the currently selected one.

Which is the behavior I expected. Only it seemed to be counting upwards away from zero as I approached the destination, not downwards toward zero. The number kept getting higher as I traveled the (correctly tracked) route, not lower.

It really does seem to have gotten its start and end points mixed up for the calculation of that number. It really looked like it was showing me distance-from-start, not distance-to-end.

The other number, the one in the lower right, correctly calculates distance to next waypoint. It's on the upper-right number that I noticed this behavior.