When I upgraded to version 9 I lost all open reminders.
Just noticed today (Dec 2) that 4 of my reminders from yesterday Dec 1 never showed up at all. A couple later in the day did. Not sure if there is a beginning of the month bug.
I shut down the client for a restart to see if this would fix the missing reminders. Instead, the 7 or 8 I left open are also now gone.
Are there new options with Version 9 that I need to know about?
Edit: I am using the Reminders window, with that option checked in Settings. Not the Windows notifications.