Deselect Auto adjust panes at run time on the navigator properties to fix the problem.
After upgrading clients to 8.5.3, navigators created with previous versions of Lotus Notes do not display properly. Sometimes the navigator does not display at all or only part of it is displayed. You can not re-size the border to show the navigator.
I read there was a fix for this because the new client written in Java has problems with the navigator but it is not fixed in 8.5.3.