I was seeing double notifications and signed out/in yesterday based on the advice above. This morning when my schedule started I started getting single notifications, and then I mysteriously started getting double notifications again. I can see it clearly in the notification center - "started xxx" / "completed xxx" / "started yyy" / "started yyy" / "completed yyy". Note that only the "started yyy" is doubled and the corresponding "completed yyy" only came through once. Weird. It's almost like it ties to send a notification, thinks it failed, and then retries.
The history in the app looks fine - no doubled entries.