cardio recovery not reported after outdoor walk

I have an Apple Watch 6 paired To my iPhone 13 mini. This week I started exploring the cardio health feature. Today I tested with a 15 minute brisk Outdoor Walk workout which captured all expected stats including time, distance, heart rate, calories, etc.

The Health app summary then showed my VO2max. But it didn’t report any Cardio Recovery data. See screen shot. I still had my watch on after ending that workout for hours afterwards, certainly including the required 3 minutes).