just downloaded xcode 9 and i\'m having this weird issue, on ios 11 my custom navbar appears to be half in size and is under the status bar, on ios 10 works fine.
so
First of all, make sure that your navigation controller's "shows navigation bar" is unchecked in storyboard.
Then, drag and drop navigation bar from the "object library". Give Top constraint equal to 20.
It'll also work perfect in "iPhone X simulator".
Happy Coding!