The section link doesn’t line up to the top of the window. Clicking the button at the bottom of the landing page takes you to the next section but you still see part of the landing page above it.
I think the issue is the disappearing NavBar as the gap looks about the same size.
You can include an anchor lower in the page to manually offset it but your probably right that it has to do with the disappearing navbar.
Another option is to modify the trigger for the navigation to show when you reach the first section, but since you already have it appearing when the user scrolls up this may conflict with that. Personally I’d rather just have the sticky navigation available without having to scroll but that’s just me.