I'm using a 30x these days and sad to report it's nowhere near as reliable when using Routes as the old Legend/Vista was. Even in off-road mode. In follow-road it's almost unusable, due to not having a menu option to switch off auto-recalculate, an option which nearly all other Garmin models old and new do have. I mostly use it in Track mode (ie Where To then select a Track) but often with added Waypoints to mark the turns, it will count down to these in Track mode just like the Legend does with a Route.
So, it sounds as though it was a 'circular' route? But that shouldn't cause a problem when you are close to the end. The E30 will always try to direct you to the nearest unvisited route point. If that happens to be behind you, it will show the (now increasing) distance to that for as long as it is closer than any other unvisited point in the list. And when you do pass the equidstance between the two points, it may still take 20 seconds or so to realise and start counting down again. No settings that affect this behaviour, as far as I know.