Do Not Disturb turning itself off

I have seen others who have a problem with Do Not Disturb turning itself on, but I keep having problems with it turning itself off on my iMac. The weird thing is that it stays turned on on my iOS devices. I haven't figured out if there is a pattern, but I have noticed it turning itself off at 30 minutes after the hour. My Do Not Disturb settings in the System Preferences app are pretty bare bones. It does not allow breakthrough notifications from anyone or any apps, but it does allow breakthrough calls from Favorites as well as repeated calls. That said, the auto-deactivation of Do Not Disturb does not coincide with any calls from anyone.

Any thoughts?