Thank you for the suggestions.
I added the filter for a specific calendar and the header did disappear. However, the first event for that day also disappeared. 
When I include calendar in the output I get the following for the header:
- [ ] start_time title MeetingLink calendar
and filtering the agenda to exclude “calendar” didn’t have any effect.
I am working in Windows 10 - do you think that has any impact on this?