Garmin 4s not recording intensity minutes for rowing

1. Activity tracking is set to heart rate zones

2. More than 10 minutes at intense (based on recorded activity)

3. Restarted both watch and app, no change

4. reset watch, no change

5. intensity minute tab is selected on ‘my day’

6. the watch did not record any intensity minutes for the activity, but did record the activity, so it is not a sync issue

7. other activities such as running not affected

Any other ideas? Worked fine years, stopped working last week

Thanks