I have a MBP running MacOS Sierra (10.12.1) and an iPhone 6 running iOS v10.1.1. Over the past few months or so, I've noticed that marking a Reminder as complete on either of those devices does not clear the notification on the other, nor does it mark the reminder as complete on the other. I'm not sure why.
Both devices are with me and using the same wifi (the vast majority of the time). Handoff is enabled on my iPhone. The Reminders app on both devices syncs to iCloud.
I can answer calls and texts on my Mac and when I open Safari on iOS, I can access the open tab on my Mac as expected. This makes me think that, generally speaking, Handoff is working as expected, but not for Reminders.
Is there something else I might be missing?