Missed activity emails

I have a user that has Missed Activity emails set to as soon as possible.  They are saying they don't get email notifications when they have their computer shutdown.  I did some research and it seems the emails are only sent when you are "inactive" in Teams.  Does anyone have details on how this works?  What if you have the mobile app installed?  Does that come into play?  Its hard to figure out when this isn't documented by Microsoft.