How are you defining the button? Can you please share your minimal sample on your OneDrive?
Both of the following buttons trigger both Tapped (and the more typical Click) for me
<Page.BottomAppBar>
<CommandBar>
<AppBarButton Icon="Accept" Tapped="AppBarButton_Tapped" Click="AppBarButton_Click" />
</CommandBar>
</Page.BottomAppBar>
<Page.TopAppBar>
<AppBar>
<Button Tapped="Button_Tapped"></Button>
</AppBar>
</Page.TopAppBar>