Before the app supported blocks, in Site home we displayed the Main menu block in the main content of the page. Because of that, we decided that if the main content already contained "Site announcements" we would hide them in the Main menu block to avoid having it twice in the main content of the page.

However, now that the app supports blocks, it's a bit weird that in LMS you can see the Site announcements both in the main content and in the Main menu side block, but in the app you cannot see it in the Main menu block.