If you inspect the partials/navigation.html.twig you can see what is happening.
Well it's doing that because there must be a child page beneath the 'home' page that is not visible. There's a navigation loop that is checking if there are children, and then if so, it displays the <ul></ul> block, but then as it loops over the children it checks visible(). Clearly nothing visible is found, so there's an empty <ul></ul> tag left, which displays as an empty dropdown menu.
This is a little tricky to fix with the loop because you need those ul's outside the for loop, but you don't know there's anything in there until you iterate over it.
What 'folder' do you have under the home folder? Is it needed? Perhaps you can make the check more specific than just .children() check.