Does anyone know what criteria the Lightning Assistant uses to determine whether an Opportunity is overdue?

The documentation page: https://help.salesforce.com/articleView?id=home_assistant_lex.htm&language=en_US&type=0  doesn't even mention "Overdue opportunity" as an option in the list - it only mentions over due tasks.

I have a user who has a single Opp listed in his assistant that says it is overdue.  This opp does not have any over due tasks, but it is open past it's close date. However the user has several Opportunities that are open past their close date - and only one is showing up as overdue in his assistant list.

So ... what criteria does it use to determine whether an opp is overdue?  I can't sort it out.

TIA!