Major Description
The RedeliveryErrorHandler needs the RouteContext to determine which onException rule to use.
The RouteContext is set at the start of a route, when leaving a route the RouteContext should be set to the route that called it. However it is apparently null, which means that if an error happens at that point it cannot use the onException rules that have been set.
In 3.0 the RouteContext was a stack so it kept track of all the routes that it passed, meaning automatically returned to the parent RouteContext value.