As the title suggests, when you add a customBreak to the navigator the labels on the axis disappear or becomes weirdly offset.
Fiddle: https://jsfiddle.net/nu5rb3g8/1/
Line 1278 is where customBreak is applied to the navigator. If you remove that line you can see the navigator X-axis labels re-appear. With customBreak set the X-axis labels disappeared.