@Garry-Davis My bad! Apologies. I looked at what you seemed to be doing but, while I’d changed the map layer, I neglected to change the default map in my settings!🤭 As a result, I couldn’t make happen what you couldn’t stop from happening. Doh!
As @Hans-van-de-Ven-MRA-Master has shown, in these kind of situations it’s usually possible to force the mapping into submission by throwing shed loads of waypoints at it! Other times, for subscribers at least, turning off ‘seasonal closures’ can work (these closures cover a multitude of sins - often not so much seasonal as temporary).
In this case, I wasn’t able to identify any particular cause. However, I messaged a friend who lives near Dingle and he says that a decision was taken ‘a while back’ to make some tourist routes one way and that the one around Slea Head runs clockwise from Dingle - counter to the anti-clockwise Ring of Kerry. I can’t see why in particular, but it seems that these one way systems have been causing havoc for sat nav users.
Also, there have been very heavy rains and winds recently, with some landslips and local road closures, though not on the Slea Head road as far as he’s aware. But maybe there could be some connected data in OSM?
Incidentally, I have found subscribing to the MRA Route Planner app well worthwhile as it does broaden your scope in some very useful ways.
I hope some of this helps following my cock up!