If I look in OSM (editing mode) - https://www.openstreetmap.org/edit#map=19/38.05150/-1.23512
and click on this roundabout, I can see it is marked as roundabout (junction - roundabout)
but I cannot find the roundabout sign/mark here, e.g.
As in this point
there is (in OSM) no restriction in turning left, Kurviger is trying to avoid Highway by using this not highway streets (without making the route much longer), with Highway option it is not doing this…
…while here
there is a restriction in turning left…
So as for me, the issues seem to be possibly connected to the information about the streets in OSM…