Ideas on why users aren't getting calendar notification emails? I've checked everything, I think.

I didn't realize a preview for the video wouldn't be created so you'd have to download it. Here are screen snips instead:
Admin/Applications/Calendars/ - the reminder hours are set this way. We don't use calendars much in our community, but for maintenance events on our data warehouse, we want clients to get an email five days before, 3 days before, and 24 hours before. 

Admin/Notifications/Calendar Event Reminder has all the templates turned on, and they're just using the standard tokens. 

I don't see any Exceptions logged on this tab.

I've impersonated users to ensure they are indeed subscribed to notifications and their settings are allowing email notifications. 

But alas...users are not getting notification emails. This is an employee, and I believe our Community has been whitelisted as an email sender, so I don't think it's an email filter issue.

Sounds like your users have enabled Calendar level notifications, but not notifications on individual events.  Is that correct?  Looking at the code, it appears the reminders are only sent to users that have turned on notifications on that specific event the reminder is being sent for.

So they have to individually turn on notifications to each event to get these? That's not how I understood it to work and not how I have been describing it. Yikes!  

So they have to individually turn on notifications to each event to get these? That's not how I understood it to work and not how I have been describing it. Yikes!