Your split nav doesn't work below 988px. That's when the nav moves to 2 lines. You're seeing this on your iPad due to its screen dimensions, but remember that it will appear like this for anybody on a smaller laptop screen or with a smaller browser window. Hamburger doesn't kick in until 800px or less.
I suggest amending your custom CSS to lay the navigation out to work perfectly at 800px. Then test it see how it grows to fit a bigger screen, rather than the other way around. Otherwise, you'll want to change the media queries to have your hamburger kick in at 988px, which feels a little large to be switching to a mobile nav, but that's your call.