I have just bought a Samsung Galaxy S7 (running Android 6.0.1) and installed the Outlook app. Email syncs fine but I see nothing on my calendar. When I tap the top left burger (?) menu "Kevin's calendar" is almost always unchecked. I check it but still nothing shows.
I have also tried resetting my account by going to the calendar settings (cog in the top right, opening my @hotmail.co.uk account and pressing RESET ACCOUNT).
I've also tried uninstalling and reinstalling the app.
It worked fine on my Android S4.