I've been testing with 100.6.0 build 2470, and the navigation is working. I switched to your production release of 100.6.0 release last week 8/22/2019 and with this release I'm getting an error
com.esri.arcgisruntime.ArcGISRuntimeException: Rerouting for the provided online route task does not supported.: Rerouting for the provided online route task does not supported.
I'm getting this error on this line of code
routeTracker.enableReroutingAsync(routeTask, routeParameters, RouteTracker.ReroutingStrategy.TO_NEXT_WAYPOINT, true).get();