By default, route centerlines throughout the tube and pipe runs assembly are hidden in all drawing views. To dimension routes correctly, recover the underlying centerlines.
You can control the centerline recovery at the tube and pipe runs assembly, individual run, or individual route levels in the active drawing view, dependent on the amount of dimensioning you need. For example, when dimensioning all or most of the routes and runs in a tube and pipe assembly, include route centerlines for the entire tube and pipe runs assembly, and then hide the centerlines for the individual runs and routes you do not need.