I figured some stuff out! The events will have goal tasks while in a scenario if a holiday isn't also scheduled for that day!
When goal tasks aren't present during the event (such as when on the same day as a holiday), the countdown timer is still present, as is the segmented green achievement bar thing (where the silver or gold coin/medallion progresses as tasks are completed), but without any tasks to complete, the only thing that shows any activity during the event is the countdown timer. When the event ends without any tasks present, it doesn't count toward completing the dinner party task in the Family Fortune scenario.
I didn't know you could set up events through the phone, so I used the calendar for this one.
Everything above was performed while in an active scenario. I'll troubleshoot some more outside of a scenario in the next day or so!