@cristiano-repetti The two routes opened fine for me, on iPad and iPhone, including the additional task of calculating a route from my location to the start of each of them. A few waypoints are slightly off road, but I don’t think that’s behind your problem. Did you create the routes in Routeplanner using the Here map? If not, the waypoint positioning is minor enough to quite possibly be accounted for by variations in spatial data between different layers.
Good call from @Drabslab there. Try turning off seasonal closures in Routeplanner settings and recalculating, then trying again in Navigation. In my experience, this causes diversions (sometimes quite odd ones!) rather than inability to calculate a route. But if there is no alternative to a given road, who knows? Definitely worth trying.
The likelihood of the latter (in fact this whole problem) occurring on many or all routes seems slim though, and I can’t help but suspect that this issue is a local one. Can you tell us what device(s) you are using, please?
Have you tried the dreaded ‘delete and reinstall Navigation’ tactic? Not something that should be at all necessary and a desperate measure but, in extremis…