Apple Watch heart rate chart not showing in activity app on iPhone

In the activity app on the iPhone, workouts do not display a chart for heart rate (says "Chart Unavailable") despite this data being displayed just fine in the Health app... any suggestions?

Only seems to be cycling that is the problem. Other workouts are fine. I've tried various different permutations of positioning and no, there is nothing in the way I'm cycling or wearing the watch that would imply poor measurement. In any case and again, the heart data is showing up just fine in the health app. Confused why it's not showing in the activity app.

There is another post in this forum that shows "resolved" but it really isn't - the conversation continued long after it was marked resolved.

Any thoughts?