I read that before writing my previous proposal, of course - but I do not fully understand the background.
But there was a similar topic with round trips on older Garmin devices: Bad GPS coverage or deviation from route @ start lead to direct routing to destination (skipping nearly the whole route). Garmin has (from my point of view) solved this with introduction of Via points and Shapingpoints: You have to reach each Via point, before the switch to next route leg is done (a leg is the part from one Via point to next Via point) - a manual switch by skipping next ViaPoint is possible.
So using some Via points in loops of the route avoids problems in round trips, trips having loops, an “8” (crossing itself multiple) and so on.
Recalculation of route during navigation means staying on same route leg - as long as you reach next Via point.
Consistent to that starting a route you can choose at which Via point to enter the route.
But I am aware of that implementing such a strategy in Kurviger App might be a huge effort, because it touches basic navigation strategy …