This popup is annoying as it doesn't last long difficult to find out Whats going on, And you cant find in in "Task Manager" as well
Try this,
Search for "Administrative tools" in control Panel and select "Task Scheduler"
Open the "Task Scheduler Library" --> Microsoft --> Office
Right Mouse Click on the "OfficeBackgroundTaskHandlerRegistration" and select Disable
And it should be gone, I had just tested again and i didn't popup
look at the Last Run Time so you know when did it was executed for last time
